Occurs on V10.13.16-B (and most likely all versions since the new sound code was implemented).
In some cases, OGG tracks may loop incorrectly. Haven't figured out the full details, but I suspect the cause is a track that lacks looping information being played after one that does have such information.
I can't consistently reproduce this bug. I did notice that on my "other levels" NXP (not quite the same as my Recycle Bin one; this one contains levels that are perfectly viable but just aren't currently in any pack, for example, my NeoLemmix Community Pack contributions and contest entries), I'd sometimes get this issue on "The Longest Minute" if it wasn't the first level played, but this doesn't always happen.
Nonetheless, I've made a change to the code that should fix this. But given that I don't know a consistent way to trigger this bug, I can't say for sure if it's fixed.