@retrobeetism I have a similar experience. #Guppe groups (at least after it went offline for almost a month(?)) rarely works all other #Fediverse platforms (those I've tried). But #Chirp groups, #Friendica forums, #Kbin magazine, and #Lemmy communities, there are rarely any problems.
My brain tells me that the issue is with Guppe platform, since all other similar software works fine. They did something to break interoperability with the rest of the Fediverse, and created its own bubble with Mastodon.