Try the following, if you have not already:
- Sign out from Creative Cloud, restart Premiere Pro, then sign in
- Update any GPU drivers
- Trash preferences
- Ensure Adobe preference files are set to read/write
- Delete media cache
- Remove plug-ins
- If you have AMD GPUs, make sure CUDA is not installed
- Repair permissions
- In Sequence Settings > Video Previews, change the codec to one that matches your footage
- Disconnect any third party hardware
Report back if anything here worked for you.
Not much time to dilly dally, but I did most of that. What actually worked was going to a previous save and NOT importing a Universal Countdown. Luckily the previous auto save didn't have the countdown and was close enough that I could rebuild the timeline. But why would a countdown cause such a major system fritz?
why would a countdown cause such a major system fritz?
No logical reason. It sounds like a project corruption issue to me, assuming you did the basic troubleshooting steps above (especially media cache deletion). You could verify that by creating a new blank project and creating a new UCL to see if the issue remains.