Your instance seems to use a beta version of lemmy so it’s possible there are API changes that make it incompatible with some 3rd party apps. Either that or the instance is being hosted behind cloudflare and the operator have strict anti bots option enabled (traffics from apps is almost similar with bot traffics). If yo ask your instance’s admins, they might be able to do something about it.

I’m not sure what that’s about. I tried with lemmy.one and had the same issue. For me it works great with lemm.ee and lemmy.world. Guessing it’s a big that’s hopefully getting worked on.