Its an oscillation so you need t change one of the inputs, (i.e. move weight forward or rearward (changes front/rear cushion pressure diff.), open the brake a tiny amount (increase losses from front comp. same effect as weight), cut a long V in the partition lower edge (about 0.5" high in centre - you can remove more but eventually you will start to lose the auto-trim functionality, and the brake effectiveness).  If it only happens occasionally then the safest option is just to crack the brake to damp the oscillation.

Every Sev that I have observed does it occasionally.

incorrect height of the divider skirt

What causes the hover to bounce like in this video?  It doesn't do it all the time.  I thought it was due to shallow water and the air pressure bouncing off of the bottom & then back up under the craft, but it also happens in deep water.  Tends to be more noticeable in flatter water.  So is it something to do with air pressure bouncing off the water surface?

https://youtu.be/wPkW9Gc7fS0