Had the same in the past. Sent money and it shows payment arrived in the bunq app. Contacted bank where I sent money, and they didn't see anything, after 20 days Bunq returned money to me after contacting support.
There is a timeline
Payment Sent - 25 Jan 2024
Payment Returned - 14 Feb 2024, with description:
RTN OF SEPA PYT FOR AMT 2500.0, V/D 2024-01-26, E2E id NOTPROVIDED, RR04, IN F/O Interactive Brokers Ireland Limited, Regulatory Reason.
Looks like something going on with bunq outbound transfers.