AAC Volume Fluctuations

Hi everyone I’m hoping you could all help me out

I’m running Kodi 17.1 on a Windows machine,
My media is stored on a nas,
I use optical cable for audio to AVR

My problem started once I upgraded from v16.x to v17

When I play a movie encoded with AC3 6ch Audio everything is fine
When I play a movie encoded with AAC 6ch Audio there is a strange volume fluctuation that makes watching impossible

The only way I can solve this problem is to disable ENABLE Dolby Digital transcode.
But if this setting is not enabled I cannot replay 6ch audio that is not encoded in DTS or AC3

Can anybody help with this problem please