I think I read there's currently a bug with Hot (and maybe active too?) sorting that can crop up when an instance is not rebooted for a while. Most people were suggesting to use the other sorting options till it get fixed, with a lot preferring "Top Day" or "New Comments".
I tried to find the discussion or the github issue back but I had no luck, if I find it I'll add an edit later, so until then take what I wrote with a pinch of salt.
EDIT: I think this is the bug report: issue#3076 and it seems someone is currently working on a fix!