I have a Beovision Avant 55 from 2015 (1st gen) and I find that the speaker has started to slide down (when it is switched off).
That is that when I switch off the TV, the speaker starts to go up in the TV, but when the TV is switched off and the speaker is almost up, it slides down again.
I have a similar problem with my Avant 55 (2016, wall bracket), slightly different. The speaker slides down when I switch the tv on, but before it is almost down, it slides up again. I read that changing the batteries might do the trick, but that didn’t solve the problem.