Hi everyone
I want to come here to explain that we are seeing the same issue with HMA and on-premises accounts.
Basically I have put it down to Acompli being rubbish.
You are all right - prod5 has more success, if you are lucky, than prod3.
Outside of working hours absolutely we see almost no problems with Outlook app or HMA tester website!
And once connected, the app is working perfectly fine.
We have also done network traces internally while running HMA tester and we see nothing at all coming in from Microsoft addresses or Acompli.
We have tried everything to rule out our side of things but this thread basically confirms its not our problem at all! We run our services via Cloudflare and Citrix ADC load balancing to our on-premises Exchange array. Disabling either of these does not help and all other Exchange services are functioning perfectly.
Please Microsoft, I assume when you bought Acompli and rebranded it "Outlook", you would have access to the infrastructure to fix this!!