Rubrics web service access problems

We're seeing lots of instances of the rubrics web services returning 401 (Unauthorized) in tomcat's access logs and we're trying to figure out why.  Other times the same url is returning 200 (Ok).

[15/Oct/2019:00:49:42 -0400] "GET /rubrics-service/rest/rubric-associations/search/by-tool-item-ids?toolId=sakai.assignment&itemId=96b8dfc8-ffc0-428b-b391-0f5ad11b2d44 HTTP/1.1" 401 163
 
...
 
[15/Oct/2019:12:57:45 -0400] "GET /rubrics-service/rest/rubric-associations/search/by-tool-item-ids?toolId=sakai.samigo&itemId=pub.585156.731604 HTTP/1.1" 401 163
 
​...
 
[15/Oct/2019:08:30:09 -0400] "GET /rubrics-service/rest/ HTTP/1.1" 401 120 

 
These calls seem like they correspond with errors in other tools indicating that rubrics returned 401.  The tomcat logs often have this message (followed by a stacktrace that indicates it's coming from rubrics):

15-oct.-2019 15:12:24.075 WARN [ajp-nio-8009-exec-321] org.sakaiproject.tool.assessment.ui.listener.author.PublishAssessmentListener.publish 401 401

org.springframework.web.client.HttpClientErrorException: 401 401 

This error occurs in Samigo on publication of a test, and the following is displayed :  "Warning: A Gradebook item could not be created for this assessment.  Please contact your local help desk for assistance".  Publishing the same draft on another server works fine, and later the same draft published on the same server works without error also!  I've also seen similar errors coming from the forums tool.
 
We're running Sakai 19.2 on 3 servers with a load balancer configured for cookie based sticky sessions.