Go to system settings and find this dialer app there.
Check if the app have permission to be "displayed above other apps", this should be not in overall permissions list but on app listing in settings itself.
Also check if it's marked as default system dialer, if there is no battery optimalization enabled and if other permissions are in place.
Go to system settings and find this dialer app there. Check if the app have permission to be "displayed above other apps", this should be not in overall permissions list but on app listing in settings itself.
Also check if it's marked as default system dialer, if there is no battery optimalization enabled and if other permissions are in place.
Hope it helps.
I allowed all permissions and removed battery optimization. It worked. Thanks