A Search Error Count is a Threshold Alert that notifies you by email that your deployment has experienced some number of search errors during a period of some minutes. This creates an Incident in the SearchStax Cloud Dashboard. Most search errors have a cause that must be located and fixed.
Custom search clients and even popular CMS products send very complex queries to Solr. These occasionally suffer from mismatched delimiters and similar syntax issues. The cause must be tracked down and corrected. Look in the solr.log files for notations about a “Syntax Error.”
Search Errors are often caused by an incomplete or out-of-date schema. The schema is the specification for the Solr index. Often the client adds fields to the CMS (such as Sitecore) without updating the Solr schema. The CMS subsequently sends queries to Solr that request matches on fields that Solr doesn’t know. Examine your solr.log files for entries that mention “unknown field,” “undefined field,” “required field,” “mandatory field,” or “Error adding field,” among others.
The fix is to update the schema by adding the missing fields, or by repopulating the schema(s) from Sitecore. Note that you must reindex your data after changing the schema.