If the app was working before it is possible that you may need to also perform an update of your AndroidOS in that device.
I would also check if there are too many apps running in the background and put them to sleep, clear caches and temporary folders, etc. with the Device Maintenance app that should be built-in with Android.
I would also perform a hard reboot, take the battery out after shutting down, just for a few seconds. Then turn on the device back on and try again.