We are aware of a Play Store bug, recently introduced by Google, that may cause our apps to get stuck on the loading screen. We have been assured that Google is urgently working on a fix, which will be deployed via an automatic update (to the Play Store apk) in due course. There is a manual fix available if you prefer not to wait.
More information is available here: https://www.androidpolice.com/2018/07/03/google-play-store-app-licensing-bug-putting-developers-horrible-spot
We also have a support article here: http://www.markstevens.co.uk/index.php/support/306-loadingscreenstuck