I submitted an error report when Corona12 was first released regarding this issue. I'm not sure if it has been resolved yet, but the 12.1 problem still persists
Can you please share your report link? (or support ticket number if it was logged as a ticket) Thanks in advance!
The solution which seems to have fixed the issue for PMVis was:
- Disabling the DOF highlights solver in Render Setup > Performance
- Enabling the "Compute after render" option under bloom and glare in the VFB
- Running the Corona Converter and converting the whole scene