I appreciate the updates that you've given, @david_g.

I want to ensure you'll be able to successfully remove the T-sheet app from your QuickBooks, so let me get you pointed in the right direction. 

To better investigate why you're unable to remove the T-sheet app, I'd recommend reaching out to our Customer Care Team. This team is the best resource for such concern as they're able to initiate a remote-viewing session to and identify what's causing the issue.

Also to give you more insights about, uninstalling T-sheets you may check out this link: Uninstall Add-ons.

Keep me posted how things turns out. I'll be to help if there's anything else you need. Take care!