Mistertango might have an automated transaction surveillance system which checks for red flags. If your SEPA transfer is captured for review, then there must be a reason. It could be the source of those funds. Was it an inward SEPA transfer from another person? They usually ask for documents in those cases. Another is, as I mentioned earlier, the amount. If it exceeds a certain threshold, then it might ring alarm bells.
The source was the same as for the first transfer which wasn't captured. I also made a third large transfer which wasn't captured. However the captured transfer was the largest so you might be right that it exceeded a limit. All transfers were outgoing SEPA. I've only loaded the account with Bitcoin.