Can't upgrade new buildings, can't place new zones

Hi

I currently have the issue that no new yellow helmets pop up even though quite a few zones are not fully upgraded yet. I can go to the residential zones ('house icon') where it says I can place 2 new zones. The moment I try I get 'can't place new zones upgrade existing ones first'. Yet there are no upgrades.

I've been following the 'requests' from the pop up bubbles for education, parks, trains, etc. All houses 100% happy, no exclamation marks anywhere on traffic, police, fire, health, sewage, waste, electricity, water, etc yet no new upgrades pop up. Have even tried bulldozing a building after which i can place a new zone that I can upgrade once (lets say from bare ground to a house). Then it goes silent again.

Unfortunately wiping the game or cache completely from my phone is not an option since it is a second city not linked to google play or such (there is an old one there I am not playing anymore).

Any thoughts of things I could do?

Thanks

R