Hello Community,

We have a strange issue with Umbraco 7.13.2, once a week site goes down because Examine media index corrupted, this error in the log -

Could not load data from Examine index for media, the app domain is most likely in a shutdown state
Lucene.Net.Store.AlreadyClosedException: this IndexReader is closed
   at Lucene.Net.Index.IndexReader.EnsureOpen()
   at Lucene.Net.Index.DirectoryReader.GetFieldNames(FieldOption fieldNames)
   at Examine.LuceneEngine.Providers.LuceneSearcher.GetSearchFields()
   at UmbracoExamine.UmbracoExamineSearcher.GetSearchFields()
   at Examine.LuceneEngine.Providers.BaseLuceneSearcher.CreateSearchCriteria(String type, BooleanOperation defaultOperation)
   at UmbracoExamine.UmbracoExamineSearcher.CreateSearchCriteria(String type, BooleanOperation defaultOperation)
   at Umbraco.Web.PublishedCache.XmlPublishedCache.PublishedMediaCache.GetUmbracoMediaCacheValues(Int32 id)

The site started to work fine after rebuilding an index and restarting the site, but what can be a reason of the problem? Why the index can be corrupted? I'm thinking about AppDomain restart and maybe writing marker is still in the index folder or something like that, but how to diagnose this issue?

Thanks, Alex