Hi Dave,
It looks like Google has marked 5 of your messages as suspicious and put them in to quarantine. I have released the ones that aren't a duplicate.
Why did they get marked as suspicious? I have no idea! Google never indicates what it doesn't like about any messages.
Do I get notified if messages have been quarantined? Yes - however, it normally takes at least 2 days before I get notification from Google that there are messages waiting to be checked. Often this means that there are multiple messages as the OP has tried several times. Sometimes the conversation has moved on since they were quarantined, and releasing the message then would be out of context and might make the poster look foolish.
How can I release them earlier? Let me know :-) Unless I know there are messages waiting to be checked I don't often check. A message to the group like this one or a personal email is the best way. Note that I am based in the UK, so I might be asleep when the message comes in.
How can you prevent further messages being quarantined? I have no idea. Sorry. Google does what Google does :-(