Scenario
Requests from dox42 Server can sometimes be throttled by D365 FSCM server. See:
Solution
You can avoid most of the calls from dox42 Server to D365 FSCM server while generating reports by using HTTP method POST or POST (Base64)(recommended).
In D365 FSCM go to System administration > Setup > dox42 > dox42 servers.
From the HTTP method dropdown select the POST (Base64) entry.

dox42 servers page