In all honesty the MS390 switches have been really buggy, and this sounds like another one of those bugs - in fact I believe it’s listed in the release notes.
I understand the concern about running beta software in production, but personally I’d consider the whole MS390 range as ‘beta’, and you will likely get a better experience with these switches on the MS15.x ‘beta’ firmware.
Just because it’s beta, it doesn’t mean it’s unsupported or unstable (unless there are warnings to that effect in the release notes, e.g. the MX17.x firmware), all it means is it’s not widely deployed (and consequently not so thoroughly tried in the field, a bit like the MS390 in general).