[Halloway]

 Just to rule out a couple of things: I tried it with the same files copied over to the local SD card and the problem was still evident. I also loaded up a SD card with 8.2.5 and played the same files from the NAS and the problem was NOT there.

Cheers,
H. 

When you say "On the latest nightly", do you mean this only started with #0526, and that #0525 is fine? Are you using any type of DAC (Hifiberry etc.)?  

 I first noticed it on #0520, 20-May-2018, this being the first Kodi 18 nightly I installed. I updated today from #0520 to #0526 and the problem was still evident. I am not using a DAC, my Pi3B+ is connected to an AV receiver via HDMI.

H. 

Did you manage to recreate this one? Has anyone else had the same problem?