Not a bug - it's an issue with your device. I'm going to assume you're on Android, in which case one of the below two options should work:
1. Free up more storage space. Android gets huffy if you don't keep a few GB of storage space free.
2. Completely power down your device and turn it back on again. This will fix any temporary driver issues that may be causing a problem.
These fixes work in 99% of cases, but sometimes it's just that there's unfortunately an issue with your hardware: Ren'py just doesn't like certain hardware configurations for some reason :/