Hi hi! When this was reported, we went through and tested each ending with challenges to make sure that they were activating properly. They were, so our best guess was that you had found a non-challenge ending.
Recently, we discovered a bug where ending challenge states were not being saved if an ending was previously seen during the same play session (without closing the game), and we're wondering if maybe that was responsible for what you've experienced.
v2.11 has a fix if you'd like to try again!