This is no big deal to me, but freaked me out at first. My Underfoot UI showed pet health bars (green group health window ones) disappear after taking a little rampage damage during the Seravince fight. The pet classes also lost their pet windows, but the pets were very much alive and commandable with /pet attack, etc.
If I had to hazard a guess, I can say that all pet classes that lost their pet windows & group pet health bars were classes that used swarm pets. This probably has something to do with the way swarm pets now pop up a conflicting pet window and override the original pet. Honestly, I'm fine with it, but it's likely to scare a few folks. I tested a few cases, and here is what is overriding real pets, stealing the window control:
**edit: zoning restores all pet windows until swarm pets are spawned again.
GH teleporters
Donor arm sune
Necro epic 2.0 clicky
Necro t8 robe clicky
Mage t8 nuke proc swarm pet
WoS pets
I *do* love the non-targeting of swarm pets, though. That's awesome!