I saw a few anons having trouble joining raids.
I do this to avoid the failed connection messages
>Ask for either a wonder trade/trainer card trade
>put a random password so you're not interrupted
>Set your field of research on "Raids"
Your raid thread should keep refreshing while searching for someone to trade with, or atleast it offers the option to refresh way more often. Just join the one that you're interested in, complete it, and repete the green text to do another one.
I've been able to join pretty much all raids I wanted to this way.