Thanks for the reply!
Those didn't seem to work for me. I put both additional recommended versions on and cleared the flags in terminal and walked through all the steps, but it still acts the same.
It does seem to be graphics-related in my mind. My work iMac Pro has the Radeon Pro Vega 64, with no onboard, so no graphics switching.
When it happens, I can move the window back to the main monitor on the iMac without restarting the app, and the interface reappears, it just will not work on the additional monitors.
If I close 3DCoat down on one of the additional monitors and restart it, it will sometimes start up back on the additional monitor and will work fine unless I attempt to resize the window or move it, in which case it will go back to the red screen. If I resize it a little bit, I get a little bit of red, if I resize it a lot, I get a lot of red, but I can never go back to a clean interface. Also, if I move it to another window I cannot get the interface back on the additional monitors (but I can on the main).
I would blame it on the main monitor being a 5k retina monitor and the other monitors being lower resolution, but my iMac at home has the same setup and it does work fine on all monitors on that system.
There is potential for my art department to switch over to 3DCoat, but I need to make sure it's going to work well for us first.
I appreciate your assistance with this!