As of the pre-patch from TWW (and on the beta aswell) Frenzied Regeneration is back down to 20% maximum health in PvP, from the recently changed to buffed and baseline 32% that came on the June 05 Tuning pass.
With the Patch Notes from June 05 regarding PvP, and I quote:
Druid
Balance Developers’ notes: We recently removed the PvP nerf for Frenzied Regeneration primarily to help Feral Druids, but Balance Druids got a windfall and became a little too powerful with this change. We’re pulling back on this buff specifically for Balance Druid only, so that their survivability is more in line with everyone else. Frenzied Regeneration heals for 5% health every sec (was 8%) for Balance Druid in PvP combat."
https://eu.forums.blizzard.com/en/wow/t/dragonflight-class-tuning-incoming-5-june/516277
I havent found any patch notes changing back the Feral druids 32% back down to 20% so this seemingly must be a bug.