/m/fedia is sort of like announcements and discussion for fedia.io itself, not so much for general discussions. You can use Lemmy Explorer to find communities that might be more relevant, though unfortunately it doesn't currently seem to index mbin, just lemmy and some old kbin stuff.
Even on local ( see newest posts at /m/test ), images with alt-text (?) seem to trigger an upload failure.
I've also been having trouble with thumbnails not being generated on the lemmy-side of YouTube links I've posted -- which I initially thought was something on YouTube's end (they made some breaking changes recently) but maybe it's related to this instead?
It's a small instance with fairly low activity (322 monthly active users reported). [edit: excluding this one] The only two local magazines I know with semi-consistent activity and >100 subs are @floatingisfun and @firefox and even the latter seems to be only sporadically active right now. The head mod of the former mag (hitstun) has done some cool local CSS stuff though!
The thing about federation is that you can subscribe just fine to communities on remote instances, so that's where you'll probably end up getting most of your feed from.
Given this is a software-the-instance-is-running request rather than an instance request as such, you might be better off posting on the (centralized 😅) mbin repo or perhaps asking about it on the mbin Matrix if they accept that kind of thing there.
Last time I checked, kbin/mbin only supports intra-instance messaging. I.e., you ( sender@fedia.io ) can message receiver@fedia.io , but not receiver@kbin.social or receiver@lemmy.world
Ended up plagued with this again for a few days, and figured it was server-side issues.. but eventually thought "why not check in another browser", so I did, and the problem was gone.
I don't know what the problem was and if it's due to kbin, the swap to mbin, is fedia-specific, or browser-specific, or some-action-that-I-took-specific, but clearing all the cookies and data in my browser for fedia.io has put things back to sane. If you read this and are having similar issues, consider trying as much (remember doing this will log you out).
I know I'm rather late on the response here, but my understanding is that each instance takes some time to discover the existence of a mag/community on another instance, particularly as it only checks the first time somebody searches for it (on that instance). I have unfortunately noticed that Fedia is often very slow for this. It took a week or two to pick up a small visual novels community I looked at a couple months back, and it still hasn't picked up @RimWorldPorn_General (SFW), which I searched for 3+ weeks ago.
Whether this is a Fedia-specific issue, a kbin issue, or something else I'm not sure. You might be able to get more input from asking on one of the larger fediverse-focused subs like @fediverse or @fediverse .