Sometimes due to the old iPhone or iPad type, there might be crashing a lot during using the app.
Firstly, make sure update your existing device to the latest version.
Secondly, use link below to clean ram to speed up the device.
https://www.igeeksblog.com/how-to-clear-ram-and-speed-up-iphone-ipad-quickly/
Finally, if it is still not working, make sure take screenshot and contact our customer service for help.