From what I've seen, Coinbase can sometimes get really cautious about security stuff, especially if there's any hint of a hiccup in the transaction. It could be a glitch on their end or maybe some network thing messing up the send. One thing you might try is contacting their support directly.
Those who have used Coinbase will know that contacting them and getting help is difficult and time-consuming. I've been locked out of transactions for 24 hours many times without finding out the exact cause, and I've been trying to contact them for weeks but in the end, they didn't help me. Then I found out that they have a pretty enthusiastic support team on Reddit, and I think the OP should contact them directly on Reddit instead of waiting for them to reply to emails and resolve the issue. But it's important to note that reddit is full of scammers, so you need to be very careful.
In addition, I advise those who are using coinbase to switch to another wallet if they don't want to get into trouble like the OP. Coinbase is actually more frustrating to use than a great experience.
