I’ve got exactly the same issue with multiple mvk files ignoring the selected audio track and playing something else entirely.
For what it’s worth this issue is only present when using the “early access” player v5.4.2, if I drop out of early access and go back to player v4.29.9 there is no issue.
It’s very similar to this issue - LG cannot play AVI files - where the “early access” player is broken while the “original” player is perfectly fine.
Server Version#: 1.20.5.3600
Player Version#: 5.4.2 (not working) - 4.29.9 (working(
NAS: Synology DS216play (DSM v6.3.3-25426 Update 2)
LG Version#: webOS 3.3.0 and webOS 4.2.0 (multiple TVs with issue)