I have, on occasion, seen this kind of response when working with HubSpot APIs. In particular, I remember coming up against this when combining create/update record calls with CRM search calls in reasonably close succession. Generally, a retry call after a few seconds has worked fine for me in the past.
Knowing that you're already using retry logic, the only thing I can think to advise would be to try extending the period of time between error response and retry calls.
Any Update On this, What is the root cause and how to prevent this. I am geeting this Error 20 to 30 time in day. i am also handling 5XX status code error and calling again same API after some time, but stil issue persist.
I first call request from my code and get exception, so go Hubspot console API Log and get reqeust body from that and call that API from Postman and it work.