Game crashes a lot more lately

I'm playing on Android phone with 1GB RAM.
I've been playing for some time, on and off, and got used to the game sometimes getting sluggish. Sometimes I exited it fast enough, at other times it rebooted my phone. I'd say it was happening more when I met the big purple crabby thing that makes by heroes panic.
Anyway, today I've unlocked the village X (10), and now the game can even crash in a middle of a mission (never happened before), and gets slow and choppy even on the first mission I play after restart. It happens even when replaying older missions.
I've killed all running apps, tried playing offline, nothing helps.
Some things that happened lately:
1. An advertising for a Weekend chest has popped up just before this started.
2. I have 8 of 12 heroes in training almost all the time. I'd say it crashes a bit more when I'm starting/ending a hero training. I wasn't playing this much before.
3. A new version of Google play has been released yesterday but I've killed Google Play.
I cannot think of anything else.

Milan