Here in the documentation it explains what the sort modes do. Active considers the time of the latest comment, and hot considers when the post was published instead.

You’ve gone full ship of Theseus.

I’m so sorry, I figured it out. In profile settings, I had enabled language english. This caused well over half the timeline, and all posts and comments in this community to vanish, including my own. After deleting those settings, the problem is fixed.

I like Geometric Weather from F-Droid. I just tried force closing it on airplane mode and it showed the same info after the close.