Web content is not displayed when connecting through the tunnel. There is 200 OK returned, but page is being rendered constantly

I have a tunnel configured with my domain pointing to one of my services
There is no firewall on server side, service is fully operational when being reached inside the LAN.

Raw http GET executed trough the curl returns 200 OK but there is no content displayed in the browser.
Web page is being rendered but finally nothing is displayed.

Service I’m trying to expose via tunnel is Synology Photos. I already submitted a ticket to Synology support but they refused it as they’re sure that the issue is on Cloudflare side.

What is significant,
while attempting trough the tunnel, my Cloudflare agent hosted on Synology docker does not indicate any traffic… no new log entries regardless if I’m sending GET using browser or curl

below there is an output from curl

*   Trying xx.xx.xx.xx:443...
* Connected to photos.xx.xx.xx.xx.eu (xx.xx.xx.xx) port 443 (#0)
* schannel: disabled automatic use of client certificate
* ALPN: offers http/1.1
* ALPN: server accepted http/1.1
> GET / HTTP/1.1
> Host: photos.xx.xx.xx.xx.eu
> User-Agent: curl/7.83.1
> Accept: */*
* Mark bundle as not supporting multiuse
< HTTP/1.1 200 OK
< Date: Mon, 28 Nov 2022 13:53:18 GMT
< Transfer-Encoding: chunked
< Connection: keep-alive
< Cache-Control: no-store
< CF-Cache-Status: DYNAMIC
< Report-To: {"endpoints":[{"url":"https:\/\/a.nel.cloudflare.com\/report\/v3?s=3T5Hb9B7PeCGSF1N4hhtAJWNZpQ%2FUYQBbG6u%2BX0MVT9U%2BJDW8pmmc18w3XL%2Bwn2mTX0HnCECZkEVSj%2FEDA9QI5Igcrs1FsSyFKw4Q2zD%2Fhy6DmipFqV636CbXmdlL%2FaBubFuHy6jVA%3D%3D"}],"group":"cf-nel","max_age":604800}
< NEL: {"success_fraction":0,"report_to":"cf-nel","max_age":604800}
< Server: cloudflare
< CF-RAY: 771396cc7e4e500c-WAW
< alt-svc: h3=":443"; ma=86400, h3-29=":443"; ma=86400
<!DOCTYPE html>
  <script type="text/javascript">
    var uri = location.pathname + location.search + location.hash;
    var URL = 'https://' + location.hostname + '' + uri;
</html>* Connection #0 to host photos.xx.xx.xx.xx.eu left intact