Mac Mail crashes when replying to some emails

I'm on Sonoma 14.4.1 and I think the issue only started after the latest update.

For some emails, and by no means all of them, if I reply to the email and click send Mail crashes. When I reopen the email I wrote has gone, it isn't in Drafts or Sent and, as far as I'm aware, isn't received.

The latest one warns me "this email contains attachments that are still being loaded" and when I click "Send Anyway" (as it would seem the attachments are never going to load, they haven't after a few minutes) Mail "quits unexpectedly".

Its becoming irritating as it only happens on important emails :)

Any thoughts?