Interestingly, I just discovered that I had encountered this bug in my last scene without knowing where it came from. I had thought that my backplate was the culprit but didn't have time to address the issue. So thank you @leo_surrealismo for this very informative thread.
The workaround seems effective, it's always better than fixing the bug in Photoshop :) but I see that the post dates back to 2021: so it's not planned to find a fix in a future Corona version?