Ideas
Hello!! Thank you so much for this tip! I cleared the cache on the EA app. I went into my save and I was able to save the lot to the gallery! So that worked, however, when placing the lot I saved, it appears blank which is consistent with what was happening originally, so I guess still a win/lose ordeal
Very strange I don't have this issue... But I tried many other things before clearing the app's cache to resolve this bug, maybe you should do the same. Know that I sorted my tray and save folders (I used an app called "Sims 4 tray importer" to save my sims, rooms and lots in an external server and deleted in my game files the ones I don't use anymore, and if I need them again I just have to copy/paste the files into my tray folder). So my tray folder is quite light, maybe it could help for saving new lots...
I also cut and pasted my entire Sims 4 folder in the external server, then restart the game to create another brand new folder and moved my save files, screenshots, recorded videos and tray folders in the new one (and deleted my mod folder as well).
Let me know if you happen to do all this and if it definitely worked !