Sorry to hear that you are having issues with using the app on your mobile phone, what type of phones are you using? Please check that the mobile device specifications are met (Mobile device specifications - DHIS2 Documentation).
This is a common error in Android OS when there are issues with the memory in the device. It might help to clear the cache of unused apps and then restart the phone. The issue seems completely because of device memory and settings so the solution depends on usage, device, configurations…etc
If you’d like to dig more into understanding the issue and sharing details that will help understanding the issue, you could have a look here: Android Troubleshooting (technical guide) but ultimately this seems like it’s an issue from the device itself, did you try different mobile devices?
I hope this helps. Looking forward to hear more.