I'll make a reply sometimes from mastodon, and I don't know where it goes. Sometimes it shows up in a thread, sometimes it doesn't, sometimes it's delayed. I don't have a good enough grip on this stuff to figure it out exactly, but I suspect it's a federation issue of some kind.
Getting into the nuts & bolts of how the federation scheme works would probably give some clues, but that's a lot of work.
I’m still trying to get the hang of it too. I thought I had, but this problem keeps me account hopping sometimes to double-check that my view is accurate.
Someone mentioned language settings, so I’m going to check that out next.