If you haven’t, shut down all game instances and check output to make sure it says the game was published successfully. If you could, provide me a game link please.
Note: it may be a development bug where you forgot to anchor things or had can collide off. Try creating a script that prints the names of everything in the workspace and we’ll see if it exists or not. If they don’t exist and we’ve tried everything, it may be a bad plugin you have installed.
If the parts are can-collide false, but not anchored, they will simply fall through everything else and be destroyed when they hit part destroy height.
This has know to be a reason for new constructions to seemingly disappear.
Make sure you check this especially if you have no terrain and the part is acting as the main “platform” for the game.
EDIT: As for it randomly being fixed, this could be because sometimes games take time to publish the new copy. After shutting down game servers, there may be a delay in publishing.