I’m wondering if this is more related to server/network issues vs. issues with app itself. With a lot of people migrating from Reddit, Lemmy instances are being hammered. I run into similar issues just browsing my instance within my mobile browser.
Based on other posts on this topic so far, it might have to do with the language selection in your settings. A few of us have gone into settings and selected all the languages and that seems to have fixed issues with posts and comments not showing up.
Unfortunately us looks to break in the other direction as well. When someone posts something and doesn’t select a langurs (or undertermined) then it doesn’t show up for others.