Model APIs: Repeated "400 Bad Request" exceptions in Instance Logs when "Show health checks" is checked

Version/Environment (if relevant):

This applies to Domino versions from 5.3.1 to 5.5.1.

Issue:

In the Model API Instance logs, when Show health checks is checked: 

After the model has been running for a few minutes, this error starts to appear every few minutes:

Exception logging request: "400 Bad Request: The browser (or proxy) sent a request that this server could not understand."

Root Cause:

This is a known issue affecting Domino versions between 5.3.1 and 5.5.1, where the exceptions appear in the Instance logs when Show health checks is checked. Note that the exceptions appear even though the model is running successfully.

Resolution:

Our Engineering Team is working to resolve this issue in Domino versions 5.3.1 to 5.5.1. The issue does not occur in version 5.5.2.

References/Internal Records:

Issue: DOM-42632