This update is a step backward. I had to just disable SmartThings integration in Google entirely.
Duplicate devices in Google due to things linked directly to both Google and SmartThings. It would have been nice to have a warning about this before the update, and to keep the old method intact until it was resolved.
Please give your vote here:
@jboaty, @jlv, @hokie, @HA_fanatic, @orangebucket, @Alwas, @Inge_Jones, @pauly
Nice idea, but 17 users against Samsung and Google power wonāt make a difference -
True, but misery loves company. So at least it might make people feel momentarily better to see that other people share their frustration. 
I votedā¦ but this is not just about Google Home integration. Itās also about Alexa integration.
Unfortunately, is bigger than that. Is the current market trend of providing simplicity over flexibility. Much like Sonos providing one HDMI on their new Arc, and alienating everyone without a TV with eARC.
So I followed the instruction on updating ST Google Home integration. I wish I had not.
One of the things that Iām noticing is the way some of the z-wave switches work. I have a few in-box mini switches that operate two loads. The parent device handler controls the mini-switch with both loads and the two children device handlers control the individual loads. ST sees 3 devices. In the past I would only expose the children to google home (in the legacy app via Google automation app) as that is really what I want to control. Now, it seems I cannot do that anymore. Instead, all Google home is seeing now is the parent device - which is useless. I would be OK if it saw every ST device as was suggested. But that is not what Iām finding.
I just re-read the note section: āChild devices are currently not supportedā.
I wish it was not a note but a warning - YOU WILL LOSE THIS FUNCTIONALITY, DO NOT DO IT UNLESS YOU DONāT NEED IT. 
my bad - the note was there.
Any thought on how to deal with this? Can I undo the new integration? Is support for child devices coming? Thanks!
You will need to make a virtual switch for each child device. You can then link the virtual switches to control the child devices with an automation in the new app. GH will see the virtual switches and will work just like before.
I stumbled on this thread because certain Harmony Actions disappeared from my Google Home app today, unfortunately. I was doing some shuffling of devices and accounts in an attempt to clean up both ST and GH apps (I have ~100 smart connected items all centralized through ST but I use Google Assistant both through Home Minis and through the mobile app for button pushing extensively). Many of my ST devices are sensors and/or not relevant for being in Google, so I was doing my best to remove them. Despite all the shenanigans and annoyances from Smart Things (which I completely agree with - theyāre doing a terrible job of maintaining features for their power user and influencer community), I have learned some useful things here and I feel the need to summarize and ask some follow ups:
Q1. As a user of ST and Google Assistant, can I granularly include only certain devices in GA?
A1. No, that feature was removed (from one or both platforms). It may return someday, but the community isnāt sure when (āmonthsā?). In the meantime a workaround is to create another (dummy) āhome/locationā in Google and relocate devices there via the Google Home application. Google hardware (Home Miniās, etc) is only able to interact with devices assigned to the same location (āhomeā). In my particular case I use this technique to prevent accidental control and to keep my app clean (organization matters when you get past a few dozen devices). Note: Google has an arbitrary limit of 5 homes per Google Account so thing wisely about your hierarchy - Iāve hit this limit.
Q2: I link Harmony to ST and in turn ST to Google. Whereād my Harmony Actions go?
A2: Apparently Smart Things Harmony Activity objects no longer show up in Google Home as a button. The objects still exist, but the only way to access them is via voice control. This is an extreme bummer for folks for a variety of reasons. Two specific examples that both apply to me (1) I want to control items without making noise in front of a sleeping baby, (2) people living in the home that are perfectly technically savvy with their personal smartphone but whom have extreme non-English accents and cannot effectively use voice commands.
Q3: How do I solve for device-name-ambiguity in the same room? For example, āSamsung TVā (the name of the Harmony-integrated appliance) vs āTelevisionā (the name of the Harmony Activity that does all the right stuff).
A3: I canāt prevent Samsung TV from existing any any of my three platforms (itās existence is required), however, I donāt actually need to control or observe it in ST or GH. Because of this Iām applying A1 from above (move this device to a dummy home such that voice commands with any word like ātvā or ātelevisionā get associated with only the proper Harmony Action).
Q4: How do I make sure my Harmony Activity appears as a device in Google Home so pushbutton controls in that application are possible?
A4: TBD [unfortunately I donāt have a good answer for this oneā¦ /me turns to look at @Lars for an official answer]ā¦ edit: perhaps the ST API is exposing Harmony Actions to Google as Scenes? I see them in Google via Home App -> Tap Profile icon in upper right -> Assistant settings -> Assisant -> Home Control -> Scenes where they default to unassigned (nothing shows under the Scene name) but they can be assigned to any room of any house by clicking on them
Harmony activities are basically stateful scenes that can interact with various devices, rather than a physical switch, so we decided to do it this way since that is supported by the Google APIs.
Now it is really unfortunate that Google decided to stop showing partner scenes in the Google Home app UI, I am still not sure why.
There is always the option for you to map them to virtual switches on ST side, but I do see the extra hassle of doing that.
Iāll bring the topic up for discussion internally.
Support is coming, sorry for the issues this has caused you.
Sighā¦ so Iāve been fighting with this all day and as far as I can tell I actually canāt outsmart Google with the trick I proposed, nor can I rename things such that trigger words go away (for example I tried to rename my television to āplasmaā AND move it to a dummy home on Googles end but the voice controls still prefer to use that item over the scene named āTelevisionā). I assume thereās some back end voodoo where ST knows a certain device is of class ātelevisionā and it passes that to Google Home.
Google may have borked things to some extend but I place the blame squarely upstream on Smart Things: none of this would be a problem if you allowed for granular item sharing. You can unilaterally accomplish this by creating [hopefully per-intecration] ACL approval. Let me go into my IDE and manually specify that a certain device should not present to a certain API (even when that api asks for everything). @Lars maybe thatās what you could propose internally? Keep this out of the GUI so novice users donāt accidentally get confused (and that saves you work). Keep the default for any new device that it DOES share everywhere, again to avoid confusion. Simple.
Agreed. Besides we did have this with the classic app function. Why remove it? I have some switches that I integrated with both GH and Smart things. Smart things would automated them for me, and GH let me control them with voice. I would exclude these devices from being exposed to GH from ST. It seems there is no way to do this now. I suppose I can āchannelā everything through ST, but it adds latency, and, in some cases, devices cannot be integrated directly. Would be great if this can be addressed. Thanks
Can we select the devices we want to hide/expose?
Thatās especially useful for Philips hue bulbs that also are shown in google assistant via hue integration
Unfortunately not at the moment.
Is there a way to revert back to the old integration until the child device support is fixed? Why would you force your users to move over to half baked implementation like this?
Iād also like to know if this is possible.
@Lars Can you provide any info on whether or not this is possible? Or even an ETA on when the child device support will be back? (Sorry to pick on you, you just appear to be the most responsive engineer in this thread.)
Unfortunately there is no way to go back. I can not give you an ETA but we have started the work on it. What devices are you guys using?
Iām using a Hampton Bay Zigbee Universal Ceiling Fan controller (https://www.homedepot.com/p/Hampton-Bay-Universal-Wink-Enabled-White-Ceiling-Fan-Premier-Remote-Control-99432/206591100) with the KOF device handler (https://github.com/dcoffing/KOF-CeilingFan/blob/master/devicetypes/dcoffing/kof-zigbee-fan-controller.src/kof-zigbee-fan-controller.groovy). The device worked fine before the login update and continues to work from the SmartThings app.
I had the same issue. I had to make virtual switches for each speed and the light. Then set up several automatons to set the speed / light brightness and turn off the other virtual switches.