[TYPO3-Solr] Custom Index on tt_content is not refreshe automatically

[Holger]

Hallo everybody,

we have Typo3 6.1.4, solr extension 2.8.2

we have a custom index on tt_content using sys_categories. 
Indexing works fine, when 

1 ) clicking in module Search on Empty Site Index, 
2 ) initialize queue and finally 
3 ) clicking on index Queue worker.

But when I just use the scheduler tasks no changes, no new articles and deletion of articles causes new indexing of the content, the progress bar of the index Queue worker always stays on 100%.
I am missing something? Do I have to add special date fields to the index?
How can I find out where something goes wrong any hints on where to look? which logfiles

We have the following index definition:

plugin.tx_solr.index {

  # für alle indizes
  # typo3 hat timestamp --> solr isodate
  fieldProcessingInstructions {
    changed = timestampToIsoDate
    created = timestampToIsoDate
    endtime = timestampToIsoDate
    sortDate_dateS = timestampToIsoDate
  }
  
  
  # definition der warteschlangen zuerst allgemein beitrag
  queue {

    # queue mit namen beitrag
    # queue beitrag aktivieren (sonst erscheint sie gar nicht)
    artikel = 1
    artikel {
       # tabelle definieren, die die inhalte enthält
      table = tt_content
      fields {
        
        ##################
        
        # Überschrift
        
        ##################
        
        title = header
        
        ##################
        
        # Text
        
        ##################        
        
        content = SOLR_CONTENT
        content {
          field = bodytext
        }
        
        

        ##################
        
        # Datum (Sortierung)
        
        ##################
        
        sortDate_dateS = sort_date
        
        ##################
        
        # Kategorien
        
        ##################
        cat_stringM = SOLR_MULTIVALUE
        cat_stringM {
          cObject = CONTENT
          cObject {
            table = tt_content
            select {
              #recursive = 30
              uidInList.field = uid
              pidInList = 0
              selectFields = sys_category.*
              join = sys_category_record_mm ON tt_content.uid = sys_category_record_mm.uid_foreign JOIN sys_category ON sys_category.uid = sys_category_record_mm.uid_local
              andWhere = ((sys_category_record_mm.tablenames = 'tt_content' AND NOT tt_content.fe_group="") OR (sys_category_record_mm.tablenames = 'tt_content' AND tt_content.fe_group=""))
              andWhere = tt_content.deleted = 0
              andWhere = sys_category.pid = 510

            }
            renderObj = COA
            renderObj {
              10 = TEXT
              10.field = title
              10.wrap = |,
            }
          }
          separator = ,
          removeEmptyValues = 1
        }
        
        
        
        ##################
        
        # Beitragstyp
        
        ##################
        typeString_stringS = TEXT
        typeString_stringS.value = Artikel
        
        
        ###################
        
        url = TEXT
        url {
          typolink.parameter = {$plugin.tx_article.artikelAnsichtPID}
          typolink.additionalParams.insertData = 1
          typolink.returnLast = url
          typolink.useCacheHash = 0
        }
        
      }
      # zusaetzliche Einschränkung, contenttypen indiziert werden sollen
      # wahrscheinlich wird text rausfallen
      additionalWhereClause = ctype IN('article')
    }
  }

Thank you very much