QUIC moves a lot of the transport into userspace and encrypts most of the header. That is good for privacy and bad for anything in the middle that used to make decisions by reading fields it can no longer see.
The practical consequence is that middleboxes fall back to heuristics
based on packet size, direction, and timing. Those heuristics are the
reason UDP is sometimes dropped wholesale on paths that
happily carry the same traffic over TCP.
If a link works over TCP and not over QUIC, the transport is usually not the problem. Something on the path decided that it does not want to deal with UDP today.