Looks like no one here had the answer yet… A lot of people in Reddit reported fixing by going in Windows settings, under System, Display, Graphics. Under Custom settings for applications, add BambuStudio if it’s not there already (from C:\Program Files\Bambu Studio\bambu-studio.exe).
Under GPU preference, select Power Saving. Some people reported that selecting High Performance worked as well, as long as it’s not left on Let Windows decide.
What I could see while debugging and going through the code it doesn’t have anything to do with the GPU at all so to speak. I have raised these questions on their github page but as usual their #1 priority is to fix new fancy features instead of fixing old bugs.
I have mentioned the problem that Bambu Lab is classified as a suspicious file on all Windows, this can cause the delays if the AV needs to scan the file all the time. Put it in exception for scanning (only if you really trust Bambu Lab)