You should really check the main log file, not the Search log. This usually happens when either
- Solr is not accessible at all,
- Solr certificate is not correct or not trusted
- or Solr wasn't ready when your CM started.
In any of those cases, you won't most probably get any error messages when Sitecore is already running, only at the beginning you will get one of those:
ERROR Unable to connect to Solr at [https://solr.local/solr]
Exception: Sitecore.ContentSearch.SolrProvider.SolrConnectors.Exceptions+SolrConnectorException
Message: Unable to connect to Solr at [https://solr.local/solr]
Source: Sitecore.ContentSearch.SolrProvider
at Sitecore.ContentSearch.SolrProvider.SolrConnectors.SolrConnector.VerifyConnection(String solrAddress)
at Sitecore.ContentSearch.SolrProvider.SolrConnectors.SolrConnector.Initialize(String solrAddress)
at Sitecore.ContentSearch.SolrProvider.SolrSearchIndex.InitializeSolr()
or
ERROR Unable to connect to [https://solr.local/solr], Core: [sitecore_master_index]
Exception: SolrNet.Exceptions.SolrConnectionException
Message: <html>
<head>
<meta http-equiv="Content-Type" content="text/html;charset=utf-8"/>
<title>Error 404 Not Found</title>
</head>
<body><h2>HTTP ERROR 404</h2>
<p>Problem accessing /solr/sitecore_master_index/schema. Reason:
<pre> Not Found</pre></p>
</body>
</html>
Source: SolrNet
at SolrNet.Impl.SolrConnection.Get(String relativeUrl, IEnumerable`1 parameters)
at Sitecore.ContentSearch.SolrNetExtension.Impl.SolrBasicServerEx`1.GetManagedSchema()
at Sitecore.ContentSearch.SolrProvider.SolrSearchIndex.InitializeSchema()
at Sitecore.ContentSearch.SolrProvider.SolrSearchIndex.InitializeSolr()
or warning
WARN IsOnline: Test connection has failed with an exception.
Type: 'SolrConnectionException',
Message: 'The underlying connection was closed: Could not establish trust relationship for the SSL/TLS secure channel.'