Act 1, Cemetery of the Eternals in party: members with different progress

I was helping a friend from PC to kill the final boss of this quest (Lachlann the Lost), while I was already on the step - quest after it.
Right after he opened the gate and moved to the NPC, I tried to teleport to town to sell/disenchant stuff but it was not possible (I got an error message), so I moved to him to face the boss.

As soon as I passed the gate, we both crashed/dced.

But for a possible global server dc, I prefer to report it, since there could be a sync issue with stages - progress during quest - campaign.