Mr. Kennedy is correct that no matter how many times you subscribe using the same e-mail address you are simply subscribed.  If you were to send 10 subscribe requests you won't get 10 copies of every message, because accounts are based on an e-mail address used when subscribing, and those accounts are unique.

There are plenty of instances where Groups.io, or any e-mail list service, or any individual e-mail user, may end up waiting a long time for a given message to make it anywhere, because all it takes is one "constipated server" in the bucket brigade to cause whatever lands on it to stay there until the issue is fixed.  The list server software itself can also encounter issues.

Waiting it out for a reasonable period of time, which is many hours to a day, is the way to go before starting to check on whether things are OK, and if they're not sending messages to any group will prove nothing, as they will be held.  Send a message to support@groups.io, and only after at least 12 hours have passed, if not more.  These kinds of "burps" simply happen, and do tend to get fixed by the powers that be.
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Brian - Windows 10 Pro, 64-Bit, Version 2004, Build 19041  

The purpose of education is not to validate ignorance but to overcome it.
       ~ Lawrence Krauss