[TYPO3-Solr] Recurring initializing problems with Solr Server

[Rumen Petrov]

Hi have recurrent connecting problems in my typo3 v4.7.9 installation.
It's a typo3 website with 8 languages (and so 8 solr cores) and several thousand pages.

The setup works so far, although i ran into that problem earlier. It helped increasing the PHP memory limit (to 384 MB).
Now i added a new root page with a new subdomain and saw the pages didn't got indexed, so i tried to re-initialize the solr connection, then again this error came up and the search works no more:

PHP Catchable Fatal Error: Argument 1 passed to tx_solr_ConnectionManager::filterDuplicateConnections() must be an array, null given, called in /html/typo3/typo3conf/ext/solr/classes/class.tx_solr_connectionmanager.php on line 338 and defined in /html/typo3/typo3conf/ext/solr/classes/class.tx_solr_connectionmanager.php line 482

I tried increasing the mem limit again but without effect.
Ealier the connection was only successful when klicking on the root page and on the "Initialize Solr conenction". The general routine at top where you can clear all caches did not work and does not throw the exception above.

Any help on that is much appreciated.