I have faced this issue while publishing in Sitecore 10.1 update 3. For me the issue was coming on making any changes in rendering and then publishing. On making changes in rendering the workflow for related test lab item lab item was getting cleared in web db. On debugging got to know that the item:saved pipeline invokes Sitecore.ContentTesting.Events.PersonalizationTrackingHandler.OnItemSaved, which queries the Web database to check the workflow status. Since the workflow is cleared, the handler encounters an error. If we publish test lab items and then the page item, error won't come.