Does it look the same in safe mode? Hold Shift when you launch TB. I faintly recall there was a similar display issue with some mail utility (Mailwasher?).

Thanks for the response and suggestion. Safe mode does not do away with the grey corner. Just to be clear, I can still see what is underneath the grey.

Could you please post a screen capture of what you are seeing? It might also be worth trying windows safe mode.

• Restart the operating system in safe mode with Networking. This loads only the very basics needed to start your computer while enabling an Internet connection. Click on your operating system for instructions on how to start in safe mode: Windows 10, Windows 8, Windows 7, Windows Vista, Windows XP, OSX

If safe mode for the operating system fixes the issue, there's other software in your computer that's causing problems. Possibilities include but not limited to: AV scanning, virus/malware, background downloads such as program updates.

Here is the gray square

Are you using Windows 7 64bit computer or updated to Windows 10 ? Is Windows OS currently up to date? Is your Graphics driver up to date? What Graphic card is used and what is last update?

Win7 Pro 64 bit.

I am using a PNY Nvidia P2000 Quadro GPU outputting 10 bit color Win7 is currently supported and up to date The GPU driver was current as of two weeks ago

GPU driver 25.21.14.1967 March 17, 2019

I have confirmed it is the current GPU driver