A PC user who switches to a PC-only avatar will show as performance blocked on Quest, even if that user switches to a cross-platform avatar afterward.
This only applies if the cross platform avatar is below the Quest users minimum performance display setting, so avatars that are properly optimized for Quest do not have this issue.
To reproduce:
Have a PC user join a Quest user with a Poor or Very Poor avatar. Then have that PC user switch into a PC-only avatar and back into the cross-platform one. This will result in the avatar being performance blocked until either user rejoins the lobby or until the PC user switches into a Medium or above ranked Quest avatar.
It is possible with flicking through Show Avatar, Hide Avatar, and Use Safety Settings with the quick menu that you can glitch the avatar to display as Medium or Excellent, which I assume is the loading and perf-blocked avatars ranks, to once again see the PC user using the Very Poor avatar even if the setting showed displayed is Use Safety Settings.