I know this problem has been documented. I have not seen a fix. Currently, I have 6 devices that were authorized to be used by IFTTT. I no longer need them so I tried to remove them in the app and on graph.smartthings.com, but they are still showing as being used by the IFTTT smart app. I’ve removed them more than once and I have checked – IFTTT can no longer see them. So why can I not forever sever the link and delete them?
Is there any way to force the device to be deleted (ignoring the test for existing smart apps)? And before it’s suggested, I am not deactivating/reactivating the channel on IFTTT – too many recipes would be affected.
As noted in the OP, “I’ve removed them more than once and I have checked – IFTTT can no longer see them. So why can I not forever sever the link and delete them?”
I’ve gone through your steps multiple times and it does not work. This has been experienced by multiple users around here and as audiorazor notes above, the only solution people have figured out is to remove the smart app and then add it back.
My bad, the method I gave is supposed to work, but as reported here by the OP it turns out there is a known bug and the method doesn’t work. Support says the only way at present to delete a device once it has been authorized for IFTTT is to contact support, give them the name of the device and the network ID, and they will be able to remove it for you.
I have added this to the list of known system issues in the community created wiki: