On Reddit you mentioned that i should try to turn some toggles off in the LUA file of the 16a version. I hope you meant those:
View attachment 653660
After turning them off, the separation into different unit groups is gone in the game but the worker bug still persists. The same is unfortunately true for the version 15 of the mod that i downloaded and tested unmodified.
And my last test was without any version of improved city view and i guess that might be good news for you? The bug STILL works... Maybe it is caused by something in improved city view, some random variable getting a weird value that persists even when you dont use it anymore. If thats not the case, the problem lies somewhere else.