We have an issue happening every once and while related to the connection between the CD servers and the solr which is causing some pages to go down and show empty results.
We found that the CM is working fine while the issue is happening on CD, and sometimes it is happening on one CD only, we checked the connection between the CD servers and the solr one and everything looks good and nothing seems related to the firewall or related to the connection between the CDs and the solr server. This is the error in the log files:
Exception: SolrNet.Exceptions.SolrConnectionException Message: Unable to connect to the remote server Source: SolrNet at SolrNet.Impl.SolrConnection.Get(String relativeUrl, IEnumerable`1 parameters) at SolrNet.Impl.SolrQueryExecuter`1.Execute(ISolrQuery q, QueryOptions options) at Sitecore.ContentSearch.SolrProvider.LinqToSolrIndex`1.GetResult(SolrCompositeQuery compositeQuery, QueryOptions queryOptions) Nested Exception
we solve the issue by recycling the app pool on the CD servers.
so not sure if this is something you experienced before?
Sitecore version is 9.2.0 Thanks