This is not about the content, but about the language setting on the post. If you didn't configure it on your account it is probably left as "undefined", which gets blocked on certain instances. Go to your profile, change the default language to eg English, and try then.
sh.itjust.works Main Community
Home of the sh.itjust.works instance.
I just figured out this exact same problem separately
I figured it was something like that. I must have to change it on the website since I don't see any settings like that in Jerboa.
The post to which I was replying was posted on sh.itjust.works Main. Why would that one post block me for not having a language set? Several of my other comment replies are also to threads in Main on here. That's where this very post is, too.
Maybe it has to do with the other users settings?
There are two settings: Interface language, and then a list of languages you choose to see. "Unspecified" and English were already on as languages I see, and I turned off German and another so I stop seeing those posts. I don't see what my "interface" language has to do with commenting, though.
I found another thread in which I had problems replying, and it turns out the comments to which I could not reply were all from kbin users.
Can I reply to my own post? (Yup)