To fix a misbehaving app, work from least to most disruptive: force-close and reopen, restart the device, update the app and operating system, clear…
A frozen app is usually stuck in a single bad state, and closing it fully clears that state.
If reopening didn't help, restart.
Crashes that started recently are often a compatibility mismatch.
Apps store temporary files (the cache) to load faster, but these can corrupt and cause crashes or stuck loading screens.
Read the complete breakdown, fixes and what happens next.