After some discussion and a remote session with the user, the final note is:
Because similar issues also appear in Arnold/Scanline without Corona, it is most likely a 3ds Max issue. We will investigate some more, for example to check if the same problems appear in 3ds Max 2023 or older. Please also let me know if you find some issue specific to Corona, or anything that happens in Corona 11 but not in Corona 10. Thank you!