When entering the Arena Tier 1 the Area Level was Lv80 instead of Level 50. The champion spawned on Wave 40 as expected though.
Encountered during Multiplayer, Partyleader was level 80, the Keyowner was Level 72. Mods after every ten waves were the correct mods for the Tier 1 Arena (“several Affix Shards”, etc.). We THINK the Monsterlevel was 80, like the area said, (because they did a lot of dmg ) but we can’t rule out that the Bug is Visual only.
Probably unrelated, but when we left the Dungeon, about half the target dummies were despawned (not only invisible, as minions didn’t attack the dummy tagged as ‘enemy’).
Edit: We can consistently reproduce this issue, but it seems the area level is not necessarily the level of the party leader, but is always the level of a party member