Unicredit and Intesa Sanpaolo occasionally block instant transfers to Bunq accounts for "security / fraud reasons". I had this problem with Unicredit and for a couple of months there was no way to make a transfer (instantaneous or not) to Bunq . To date it works without problems, it may be that they have reintroduced the blockade. If you contact support, they will probably tell you that Bunq has been blacklisted.
With Intesa Sanpaolo, on the other hand, I advise you to go on to make the bank transfer to "get used" to the system for foreign operations and then you should no longer have problems, at least in my case it was.