OK, I figured it out! I was using both an old version of SkyUI and SKSE. Upgraded to skse 6.1.6, SkyUI 4.1, and still the groups disappeared when I transformed to VL form ... however, now, when I revert form, they're back! Groups would not logically be available in VL form anyway (they're for changing equipment, which VL isn't using), so this fixes my issue. Hope this helps someone, although from your initial post it seems like you already tried upgrading. By the way, I'm not using BOSS.