Failed to start managers. java.util.ConcurrentModificationException

Hi,

if i restart the tomcat, sometimes one of the JSPWiki's won't come up again, due to java.util.ConcurrentModificationException.

Any ideas?

I have about 16 JSPWiki's on one server. Is it simply too much?

Tomcat Version 8.0.22

JSP-Log:

2016-03-03 04:31:23,386 [wikiland.de-startStop-1] FATAL org.apache.wiki.WikiEngine - Failed to start managers.
java.util.ConcurrentModificationException
2016-03-03 04:31:23,387 [wikiland.de-startStop-1] ERROR org.apache.wiki.WikiEngine - ERROR: Failed to create a Wiki engine, stacktrace follows
org.apache.wiki.api.exceptions.WikiException: JSPWiki: Unable to load and setup properties from jspwiki.properties. Failed to start managers: null
2016-03-03 04:31:23,460 [JSPWiki Lucene Indexer] ERROR org.apache.wiki.search.LuceneSearchProvider - Unable to start lucene
java.lang.IllegalStateException: Can't overwrite cause with java.lang.IllegalStateException: Illegal access: this web application instance has been stopped already.