Although set a ring tone for signaling incoming VoIP Calls only once the tone is played

On Android 9 and 10 i have several clients set with an individual ring tone for signaling incoming VoIP Calls.

When a call is started the participant only hear once the signal for new Element Messages and that's it. The Banner on Top of the screen that indicates that the Call still waits to be established resists silently. The called person can join the call formerly without problems.

For a secure reach of a called person it is nescessary that this person has permanently a look at his / her device to see the silent Banner Message for incoming call. (a loud indication of the call is missing)

If you wear the device in your pocket and don't carefully listen to the one time notify for the call, you will miss the call.

I changed the settings several times on different clients without success.
It does not make any difference, if the mp3 or wav sound comes from an external storage (sd card) or from the internal storage of the device itself.