Server crash - Penitentiary map (start of boss fight)

My party of two have crashed the server twice in a row on this map. Steps to reproduce:

1. form a part (we're using two players, both disciple of varashta)
2. enter Penitentiary map (T15, 6 modifiers)
3. enter boss arena (executioner fight)
4. Pre-channel Kelari's judgement (in anticipation of boss)
5. boss hops down from head-chopping platform :), as soon as he becomes active (health bar appears), server crashes (all players are kicked)
6. Upon logging back in the map portals are gone and the atlas shows the map as "failed" (tablets may not be applied to maps that were previously attempted).