Thanks for your feedback.
Are you able to reproduce this issue?
This is a known Android OS issue which can be replicated on other Android apps. We are hoping that it will be fixed in future updated.
You'd have to join the BETA program to get this update.
Just launch the Play Store, search for 3CX, and while in the Apps information page (where you see Uninstall & Open) scroll down to where it reads "Join the Beta" and press "Join".
It may take a few minutes but once complete you will see the Update button available for you to install the latest Beta app.
At any time, you may leave the Beta program by following the same steps to where the app information page reads 'You're a beta tester' and tap on 'Leave'
Should you still reproduce the issue, please let us know, together with your phone brand, model and Android version