One thing I read about a while ago (can't find the link at the moment) is that QUIC doesn't play well with firewalls that do QoS (at least, by default), because a node will send as much UDP data as it likes and the system has to deal with it as it comes in; with TCP, you can adjust the window size, etc. to slow the transmission rate, and so on, but current firewalls don't have any (practical?) way to manage this.

I solved this issue at my last company by just blocking 443/UDP at the firewall so that clients (i.e. Chrome) would fall back to HTTP/2.