Android 9 Bluetooth - skip/play/pause keys does not work

[Stefan1200]

Plan

Premium

Spotify version

8.5.32.889

Device

HTC U11

Operating System

Android 9

My Question or Issue

Since some months I have the following issue:
My phone is connected with my Kenwood DPX-7100DAB car radio and use Spotify to play music. The music title and artists will also be displayed on the car radio.

But the play/pause/skip buttons on the radio are not working anymore. Sometimes the skip button is working only once. I never had this issue some months ago (using this combination since one year, the first 8 months without problems).

It have no effect, if I enable or disable the car mode of the Spotify app. I also reset the bluetooth settings and deleted all bluetooth pairings in my Kenwood radio and on my Android 9 phone. But I have the same issues after repairing.

Other music apps on my Android phone don't have problems with my Kenwood radio, all buttons are working fine. Any ideas or solutions?