I have been noticing a number of posts missing from my subscribed feed. I went and looked at my community !left_handed@sopuli.xyz and in Mlem no posts are shown. However, if I visit the website, or view the community through other apps there are posts, as well as the missing posts from my subscribed feed.
You can show/hide read posts from the ellipsis menu in the top right of your Feeds tab.
Thank you. I must have turned it on one night when there was a lot of spam posts and forgot about it.