This seems to be random. These are communities on the instance I’m logged into. AFAICT I’m not being blocked in these communities. I’m not even sure if mods *can *block someone from seeing a community. I’m guessing this has been asked before, but I couldn’t find a thread on it.
Do you have your languages set to both “Undetermined” and “English” in your settings? I had a problem seeing some posts with only one language selected.