Bridge full screen preview makes my screen glitch out

I am not sure if this will help but since you mentioned that you're working on an external HD, please try the following:

Go to your System Preferences and select Security & Privacy. Click on the Privacy Tab, then scroll down till you see Full Disk Access.

Then unlock the lock in the bottom left with your system authorization PW. Finally click on the “+” to bring up an Open window and select LRC and any other applications that needs or may need open access to various areas of your computer. 

But wait, there’s more…

Now click on the next folder down, Files and Folders. You’ll see many applications grayed out because these are applications that already got permission from the first part.

But as you scroll down you may see other applications that have sub-categories to OK. If that lock is still open, you can do this at any time.

Close everything up and you should be good to go.

Which OS?

Do you have the latest video driver installed?

Laptop or Desktop?

Moving post from Community Help to Bridge.