An error occured during index rebuilding. There will be another attempt to check

Question

Getting the below error message while rebuilding the index

SourceContex - Sitecore.Xdb.Collection.Indexing.Rebuild.IIndexRebuildFlow

System.Net.Http.HttpRequestException:
   at System.Net.Http.HttpResponseMessage.EnsureSuccessStatusCode (System.Net.Http, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a)
   at Sitecore.Xdb.Collection.Search.Solr.SolrClient+<PostXmlRequestAsync>d__6.MoveNext (Sitecore.Xdb.Collection.Search.Solr, Version=3.1.0.0, Culture=neutral, PublicKeyToken=null)
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw (mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification (mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089)
   at Sitecore.Xdb.Collection.Search.Solr.TaskRetryHelper+<>c+<<ExecuteTaskWithRetryAsync>b__1_0>d.MoveNex
   at Sitecore.Xdb.Collection.Search.Solr.IndexRebuildHelper+<CleanRebuildCore>d__11.MoveNext (Sitecore.Xdb.Collection.Search.Solr, Version=3.1.0.0, Culture=neutral, PublicKeyToken=null)
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw (mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089)
System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification (mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089)
   at Sitecore.Xdb.Collection.Search.Solr.IndexRebuildHelper+<PrepareRebuildCore>d__8.MoveNext (Sitecore.Xdb.Collection.Search.Solr, Version=3.1.0.0, Culture=neutral, PublicKeyToken=null)
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw (mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification (mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089)
   at Sitecore.Xdb.Collection.Indexing.Rebuild.IndexRebuildFlow+<RunRebuild>d__25.MoveNext (Sitecore.Xdb.Collection, Version=3.1.0.0, Culture=neutral, PublicKeyToken=null)
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw (mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification (mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089)
   at Sitecore.Xdb.Collection.Indexing.Rebuild.IndexRebuildFlow+RebuildStatusWatcher+<>c__DisplayClass5_0+<<Start>g__RunRebuildFlowCycle|0>d.MoveNext (Sitecore.Xdb.Collection, Version=3.1.0.0, Culture=neutral, PublicKeyToken=null)
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw (mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089)
   at Sitecore.Xdb.Collection.Indexing.Rebuild.TaskExtension+<ExecuteWithInterval>d__0.MoveNext (Sitecore.Xdb.Collection, Version=3.1.0.0, Culture=neutral, PublicKeyToken=null)

Answer 1

1. Firstly, suggest that to check the solr logs for more details on the underlying exception and failed HTTP request.
2. Ensure that's not network connectivity issue ,like CD/CM server with solr, or client timeout issue.
3. if above is not ok ,you can try to restart the solr service and re-initiating the rebuild.
4. If it continues to fail, you may need to reset the core and re-index from scratch.
5. Open a Sitecore support ticket if still not resolved.