Never mind, the “problem” didn’t repeat on the next delve level.
Beating the boss battle gives the final chest increases. If you had level 3 before the last fight you should have had level 5 after because the boss room gives a guaranteed +1 and then your bonus for defeating the boss room which for you is another +1.
That’s the way I figured it and it didn’t seem to happen. I’m working on another level now and will note the chest level before the boss battle.
OK OK. Before the battle it was a level 3 chest. After it was a level 5 so there’s no issue.
Everybody ignore this thread!