[TYPO3-Solr] Indexing Queue: Failures: Where to see what goes wrong?

[Beta Patch]

Dear all,

I succesfully installed solr for typo3. It seems everything is working.
Except, when I look at the indexing queue task in scheduler there are always 47 failures.
Where can I see what is going wrong, and which pages are not indexed?
I didn't find anything in the T3 system log, nor in the developer log nor in the apache log files.
Where are this indexing failures logged? And what exactly does a failure mean?

Best,
betapatch