Ideas
I got a new laptop last month so started with a completely new install and save file. Went through world by world replacing all lots and by the time I got to Ciudad Enamorada, I noticed that lots I had placed in Willow Creek were disappearing/reverting back to defaults. Checked all the other worlds I had done and it was happening in them too. I removed all mods/cc and disabled script mods in my game options, as I thought it was a mod issue after the August update, but it was still happening. Stumbled across this For Rent save issue on a google search, so went through and changed all my Residential Rentals to normal Residentials and it immediately solved the issue. Seems like you can't have Residential Rentals if you build on all lots in all worlds, like the game can't handle it. I started out by limiting the number of Residential Rentals in each world, but as I got further with my rebuild, I eventually had to evict all renters and remove Residential Rentals completely. Doesn't matter if you place different types of lots in each world (nightclubs, restaurants, cafés, parks etc), as long as Residential Rentals are placed, any other lots disappear/revert back to default.