I noticed not all comments are visible in the app. Sometimes not even my own. E.g. I'll see a post with reported 40 comments, but when I open it, only 5 are visible. Oftentimes when I reply to a post, I don't see my own comment. I don't have this issues in my instance in browser and another Piefed/Lemmy Android client, so it's definitely a Boost bug. Not sure how to help troubleshoot it.
I've seen this occasionally too, but always assumed it because my instance was de-federated from the commenters instance.