Custom Taxonomy not added, arbitrarily

FeedWordPress version 2013.0504.
WordPress: version 3.9.1 (Fresh installation with no hacks, etc)
PHP: version 5.4.12
Web Server: Apache/2.4.4 (Win64)
WAMP Server (test server, not online)
———–
Implementation:
– Added 20 syndication links (RSS Feeds).
– Each of which has 5 items in it.
– period of update 1 hours (updating Simultaneous).
– Feeds are all local (a copy of 20 remote xml feeds are created localy every 1 hr ).
– some parsing made to the local feed copies on creation/update (like removing unwanted content, etc).
– No FWP addons are installed.
– No FWP filters are applied.
———–
Noticabled change to WordPress:
– Just added a Custom Taxonomy, called sources like this:
register_taxonomy(‘sources’,’post’,array(
‘label’ => ‘sources’,
‘rewrite’ => array( ‘slug’ => ‘sources’,’with_front’ => false ),
‘show_admin_column’ => true)
);
– added the Automatic Post Tagger plugin.
———–
Problem:
the problem is that, some times, for some posts, from some synsources, the sources custome-taxonomy not added to the post, and since each post has just one term for the sources taxonomy, it is left empty. I could not find any pattern for that , and as I mentioned, it is totaly arbitrary. some times for source1, some times for source2, … and just for some their posts, the source is not added to the post.
———–
Extra Information:
– Any additional information could be delivered if needed (like settings, any other changes,…).
– Comments are disabled.
– I use tags on each post, using the nice Automatic Post Tagger plugin.
– My wordpress is local and is not online.
———–
Question:
– What’s the cause?
– How can I fix it?
– Is this called a large implementation(20*5 items each 1 hr)? If yes, has the problem anything with it?
– Are there any tweaks to improve performance, regarding that I dont want any change tracks, revisions, history, etc.? I just want some post to be placed on my db, and I dont care for the correctness and revision so much.

So many thanks for your help and consideration 🙂

https://wordpress.org/plugins/feedwordpress/