I've found that pinned posts that are ones will always be on top. There was a bug where some posts unpinning did not federate properly, as I recall. It may not be the fault of boost

Are you filtering out previously read posts? Maybe you've already seen all the more recent posts...

Found out this was happening due to me having the "show read" setting turned off in my account settings. Turns out read≠hidden... That kinda make the clear read function useless if I can't easily decide when I want to see things I've already seen before...

This also happens for me with most communities but not C/boostforlemmy apparently

I haven't noticed this behavior. Do you have steps to reproduce it?