ReadyAPI LoadAgent error "Failed to set the project environment."

We are using LoadUI in distributed mode and sometime some agents throw the following error  "Failed to set the project environment." and any test that target that agent fail with an "endpoint is not defined" message. 

The project only has one environment specified. 

We can mitigate this problem by restarting agents but this is blocking our ability to add some load testing in to our automated build / deploy pipeline.

Has anyone had any experience with this error and what the cause(s) of it could be and how to fix it instead of just mitigating as we do now?

Steve