Many of us are having problems with Dolby digital and DTS audio dropping out over both HDMI and optical I believe. Does any one know if this has been fixed in V18?
You could try and test the new Kodi 18 Beta 5 build, and see for yourself if it solves your problem(s)...
Is it possible to install this along side a stable kodi or run from a memory stick to test as I dont want to overwrite my current version that is functioning perfectly well aside from the audio drop outs.