[TYPO3-Solr] Index queue scheduler task doesn't start/re-start automatically

[Thomas Schilling]

Index queue scheduler task does never start or continues if started
manually. I'm using a fresh new installation (V. 2.2.2), tested on three
different website installations (Typo3 4.5.17 and Typo3 4.7.2) and
servers.

I tried several hints to solve the problem like clearing all temp_CACHED_
files or truncating tx_solr_indexqueue_item. Re-installation of
apache_solr didn't help either.

Everything else works fine (after running the scheduler task manually).

All tested installations use RealURL, might this be an issue?