Is this error reproducible when sending a specific request body? Or are you seeing these errors sporadicaly? If they're reproducible, can you give me your Hub ID (and App ID, if applicable) and an example request body you're sending?
That's extremely helpful information, thank you. Last question while I dig into this: Are you seeing any sync errors related to the pipeline_id property? Or are you only seeing these errors in the response when sending sync messages?