[2020] Is there a "Not enough..." bug?

"Not enough buyers" pretty much means "my internal storage is full and all my delivery trucks are busy." Since you have it along with "Not enough raw materials" I wonder if you're hitting the vehicle limit. If your buildings' delivery trucks were just all busy, then cargo stations/harbors/airports should have helped the problem some at least. And since you have TMPE with no despawning, it is at least possible you're hitting the limit.

You can get CSL Show More Limits to check how close to the vehicle limit you are. If you're close, then your buildings are likely unable to spawn delivery trucks at all until some other vehicle despawns. To fix that, you'd need to lower vehicle usage, which is usually done by having lots of efficient public transport, paths and bike paths.