At least is was fixable by disabling steam cloud. I think one of the mods I used somehow incorporated itself in the save pretty fundamentally and whenever steam synced the save back I ended up with some kind of mod remnant in there.
That said, tunnels are yay (still no weather though), but those European buildings are not very yay. In fact I think Collossal Order took the lazy approach just looked at images of Berlin and Paris and made them by that, but most European cities look VASTLY different compared to the (nearly pre 1939) style buildings that are now in. Also considering back to back buildings are a real thing in Europe, they failed to actually code something in to make sure that T and L shaped buildings properly line up with the other T/L on the opposing road side in a normal 8x8 grid, so yeah... they do not line up, so this looks very weird. In reality obviously back to back buildings are back to back, not just side by side like the game currently does it. So in essence the game doesn't actually have back to back buildings. It has models of buildings that sometimes, rarely, align properly, and oftentimes do not. Making it look very very ugly.
So imo of course, this european style "addon" is free, and has exactly that quality. It actually looks exactly like something you could already have had (even made by yourself) if you had downloaded mods with back to back buildings. But there is no logic in the game to make sure buildings line up right.