Hi joolzlover,
If you are running low on internal storage space, it is possible that apps may be removed unexpectedly.
If you have seen any low storage alerts, the steps here may help you create some space:
How to check the storage on your iPhone and iPad - Apple Support
If you storage seems to be adequate, we recommend restarting your devices and keeping them updated as those steps assure you have cleared out any minor software issues and are running the most current version.
Restart your iPad - Apple Support
Restart your iPhone - Apple Support
Update your iPhone or iPad - Apple Support
If you still have questions, reach out to Apple Support directly, as this may require closer guidance: Get Support
Cheers!