KODI 17.3 No Sound when switching from 5.1 source to 2.0 source

Hi there,
I’m currently using Kodi 17.3 on android media box (Venz 10), connected via optical SPDIF to the sound system and HDMI to the TV. Up until the update to Kodi 17 I had no problem but ever since whenever I watch a movie (DD or DTS 5.1) and then try to watch a TV episode (2.0) there is no sound at all. I have to unplug and restart the android box to get sound again … and if I watch another movie the same problem occurs … there seems to be a problem with Kodi recognizing the switch to new audio keeping the 5.1 configuration. Any ideas? Thanks in advance.