Boss fight didn't trigger in Crypt - Tier 14 map

Upgraded a magic Tier 14 map to rare, has the following affixes on it:
Increased magic pack size
Area has patches of shocked ground
More monster life
Increased pack size
Increased quantity of items found in this area
Increased rarity of items found in this area
Increased waystones found in area

Cleared map, 1 monster remains.
Tried to portal from large area, message appears "Portal disabled in boss fights".

No boss fight appears, unable to complete map.