Hmm. I think i sorted this out a while back.
I'm fairly sure it doesn't happen in 0.28, but I do not have any older save files to check with.
Is it possible to send me your save file?
I may be able to sort out some lingering backwards compatibility issues.
Viewing post in Hom Factory : My Monster Girl Tower comments
Android build has always had issues after a certain point.
I've tried to pin these down, but it really seems like a phantom bug associated with the build process.
As such, I've stopped updating android versions of the game. Instead, you can use Joi Play to play on mobile.
Check out the latest release post (or the main page of the game) for instructions on how to set up Joi Play.