The only reliable way I’ve seen to trigger a fetch is to enter the community URL (e.g. https://midwest.social/c/projectzomboid) or the ID (e.g. !projectzomboid@midwest.social) in your Lemmy instance’s /search page.

This matches my experience exactly, though only one user has to do it and if someone else does the search while you’re messing around with other things it can occasionally FEEL like something else did it but then it won’t reproduce a second time.