Hi there, @kmetro.
It's good to know that you've exhausted all possible troubleshooting steps to isolate the issue. I understand how important it is for you to sync FSM to QuickBooks Desktop and I'm here to ensure you're getting the right support to get this fixed.
Since the same thing happens even after doing all of the processes you've mentioned, I recommend reaching out to the Corrigo Pro Specialist Team. They have all the necessary tools to look into this issue on their end and find the root cause of this matter. Know that they can only accommodate you from Mondays to Fridays from 8 a.m. to 8 p.m. ET. To know how to contact them, utilize this article: Intuit Field Service Management Setup and Support.
Moreover, you can always browse some of our Helpful Articles that will guide you through completing your tasks in QuickBooks Desktop. This includes integrating Desktop to other QuickBooks platforms.
Feel free to comment below if you have any additional QuickBooks-related matters you'd like to talk about. We're always glad to help and assist you with the information we have.