Ren'py and Android don't always play well together - certain combinations of hardware and OS version can cause crashes, freezes and assorted glitches.
The only three things that have been known to help in some cases are:
1. Free up more storage space on your device
2. Make sure your device is fully updated
3. Fully power down your device and restart it
Sorry I can't be more help, but this is an SDK/device issue and so I have no control over any of it :/