Does Coinbase have a feature to send from one account or another? Are you using his email, or some kind of tag? If so, and although I doubt this would work you can try is to send to a non-custodial wallet of his, and see if that works or changes anything.

According to this [1] all operations seem to be normal. So if the above doesn't work, your only hope would be to contact them

[1] https://status.coinbase.com/