Why is the HTTP/3 + QUIC not working on my domain?

My server setup is as below:

Apache → Varnish → Nginx
HTTP/2 from origin server.

Headers I get on the site is as below from (https://http3check.net/):

HTTP/1.1 200 OK
Date: Fri, 10 May 2024 06:02:47 GMT
Content-Type: text/html; charset=UTF-8
Transfer-Encoding: chunked
Connection: keep-alive
CF-Ray: <>-EWR
CF-Cache-Status: HIT
Cache-Control: max-age=86400
Last-Modified: Wed, 08 May 2024 17:36:46 GMT
Strict-Transport-Security: max-age=63072000; includeSubDomains; preload
Vary: Accept-Encoding
Via: 1.1 <> (Varnish/7.5)
cf-apo-via: tcache
content-security-policy: frame-ancestors ‘self’; upgrade-insecure-requests;
cross-origin-embedder-policy: same-origin
cross-origin-opener-policy: same-origin
cross-origin-resource-policy: same-origin
referrer-policy: strict-origin-when-cross-origin
x-cache-hits: 305
x-cacheable: Yes:Cached
x-content-type-options: nosniff
x-frame-options: SAMEORIGIN
x-varnish: 1345947 395527
x-xss-protection: 0
Report-To: {“endpoints”:[{“url”:“https://a.nel.cloudflare.com/report/v4?s=7txrlKrStWunx8%2Bw8SpQF<>nhp%2B5Y9RU%3D”}],“group”:“cf-nel”,“max_age”:604800}
NEL: {“success_fraction”:0,“report_to”:“cf-nel”,“max_age”:604800}
Server: cloudflare
Content-Encoding: gzip

I’m on the Cloudflare Pro plan too and yes, have enabled HTTP/2, HTTP/3 + QUIC in panel.
Already tried turning it off/on, clearing cache (both Cloudflare’s and Varnish’s), no luck.

A sidenote is that this was working fine a few months back and I did not change any settings or setups either.