Brewfest event. Phasing? Server changing?

Hello,

Doing Brewfest... one toon logged out during the fight. The others won the fight. When that toon got back in, there was no gear, and the rest of the team was phased. I logged onto an uninvolved account and it was phased with the toon that got logged.

Is this something the did to the event?

Or is this a generic thing they to do "balance servers" ?

And, relatedly, my mage just teleported out... and when she got back, the group was phased.

Any intel on what Blizzard is doing, and how I can keep my team together. (And ideally those outside my team, as well.)

Team is partied. Strays typically are not.

Thanks.