Fortiproxy allows traffic, then it denies it...

[kuchenmann]

I think this Fortiproxy is a big sh...
It allows traffic most of the time, and suddenly it denies it with useless information "UTM Blocked".
Deep Inspection already disabled for destination.
So how can it still block it, it can not look inside the SSL-traffic?

[ethopwa]

How are users authenticated? Does authentication work the same way internally and externally?

You could even have different proxy policies based on if they are internal or external. Try to use the forward log to see which policy is blocking it and why https://speedtest.vet/  .