You wouldn't be alone in the world in thinking that you were being blocked / moderated / censored with groups that you were a part of because of Yahoo's lameness. I don't know how long you've been on Yahoo Groups for but I've been on this thing for at least the last 15 years and I think a great proportion of Yahoo Groups users would never know how bad it's gotten.
It used to be an email reply was very quick, certainly much quicker than logging in to post via the web interface; now, well the last email reply I sent to a group I'm on took 4 days to appear. The post I made here before was done via the web interface and that took about 20 minutes to appear. Hardly the lightning service it once was.
I'm willing to bet in a few days your original posts will appear here. If not, Yahoo lost them - it happens!