There are definitely community members who have several hundred devices, including over 150 physical devices. @johnconstantelo might have more to add.
@bamarayne also has well over 100 physical devices, and I don’t think he’s been seeing any particular problems lately.
Apparently support has recently been telling people who have more than 40 Z wave devices not to run a zwave repair if they’re having network problems. That seems weird to me, as I’ve expressed, but it is what it is. A zwave network has a hard stop at 232 devices because of the addressing scheme, but I wouldn’t expect to see specific problems below about 150 Zwave devices other than system utilities taking a long time to run. But of course SmartThings is a cloud-based platform, not pure zwave, so there are a lot of idiosyncrasies.
Separately, I know you’re already active in the thread that I’m about to link to, but for anyone who finds your thread first, there have been multiple reports this month of people who are seeing lots of different weird errors. It’s not a huge number of people, but it is more than a dozen at this point, so I don’t think it’s just individual hub failures or mesh strength issues, although it could be. Particularly since all of these reports are from people who had set ups that were working just fine and then suddenly multiple things started failing.
But for those who are having issues with multiple devices going off-line and multiple automations failing to fire with problems that just started in June 2017, you can start with the following discussion thread: