For the given URL I see the same issue.
I checked with tcpdump and I see communication to the webserver:
- SYN - SYN/ACK - ACK - GET Request - ACK --> Nothing happens (no answer)
After some time the communication starts again with the same result.
After the third try the web gateway gives the 502 error.
From my point of view the webserver has an issue with the "Get Request", but, for now, I cannot figure out why.
I created a Support Request and got the same answer than yours. Good to hear that it seems not to be misconfigured on our MWG.
We captured packets on our Outer Firewall and got the same result (Get - but no answer). Also we tried to connect over Fortigate Proxy - Same result.
Thank you freddykr.