if you're not community banned you might still be instance banned on the community instance, which wouldn't show up in your local instances modlog if the ban happened on a <0.19.4 instance. if the methods pointed out by other comments here fail I suggest you visit the instance of the community and check the site modlog there, searching for your user.
i suspect you're referring to your post to a lemmy.ml community and you have indeed been instance banned there for a limited amount of time.
Do you see the content of these communities when logged out (ex: incognito mode on your browser) or through another instance / the home instance of that community?
One possibility is that the instance you're on "deleted" the remote community, and it won't sync anymore until restored.
We had to do this with a couple of unmoderated communities filled with spam, with an unresponsive instance admin. It was that or defederate completely from that instance, which I'd rather not do.
You need to be sure your instance in federated with the instance that you are engaging with and visa versa. It is always listed on the ../instances page. So your host is:
It's always a bad feeling when you thought something was wrong with the server and you have NO IDEA you were banned from the entire website without any kind of confirmation, but can somehow still have access to it as if you're logged off.
If anyone suspects anything, they can test it out by messaging me, I don't bite. Give a marco and get a polo. I'm tempted to ask, can those who don't know anything is up really be blamed if they re-register (considering it's evasion)?