summary for normal people: if your projects aren't saving, log out and back in again (you can log out/in on another tab to prevent losing your work) read the project "the project.json servers" = the servers that store the project.json of projects, which includes code, variables and metadata about sprites and assets. as such, if you don't modify or add any costumes or sounds, your project will save just fine without needing to log out and back in
credits to griffpatch's project telling users about the bug itself i guess, that's how i found out about it (i don't use scratch that much) https://scratch.mit.edu/projects/1045489299