While connecting Sitecore to Solr Cloud, some clients encounter a problem trying to populate the schema used by the Sitecore collections. It often looks like this:
This occurs when Sitecore has been configured to use only one schema for all collections, and the user tries to populate it from all of the collections at the same time. This creates a race condition where many of the updates time out and are not included in the schema.
Using the SearchStax Sitecore Plugin obviates this situation by creating a separate schema for each Sitecore collection. The critical setting is isUniqueConfigs : “true” in the configs.yml file. If you change that value to “false”, you are inviting the race-condition bug.
The easy work-around is to repopulate the schema by adding one collection at a time from the Sitecore interface.