Plugin works sometimes, not always

I can’t post a link since I have installed this plugin on a local wp install.

I’m using the plugin to cycle through random posts with a specific tag and category. There are 2 post categories and 7 tags. This is my url:
mydomain.com/?redirect_to=random&cat=47&tag_id=56&each_once=rewind

For now each tag has 10 posts in it (will be 150 on final version). So it should cycle through those 10 posts randomly until it’s gone through them all.
For some reason it always jumps to the second to last post, then to a random post, then back to the homepage.
It does this for all the tags. This doesn’t always happen. About 50% of the time the plugin works, the other 50% it doesn’t.

All the posts are published, there is no caching plugin.

When I add &rutpdebug=2 to the end of the url, I get this:

Picking each random post only once.
We use redirect_to=random.
Query parameters:

array(9) {
  ["cat"]=>
  string(2) "47"
  ["fields"]=>
  string(3) "ids"
  ["ignore_sticky_posts"]=>
  bool(true)
  ["order"]=>
  string(4) "DESC"
  ["post_status"]=>
  string(7) "publish"
  ["post_type"]=>
  string(4) "post"
  ["posts_per_page"]=>
  int(-1)
  ["suppress_filters"]=>
  bool(true)
  ["tag_id"]=>
  string(2) "56"
}
We found 10 matching post(s) in the cache.
We picked a random post.

So, it ‘sees’ all the posts, it just doesn’t cycle through them.

For some reason, after I add &rutpdebug=2 to the url, reload the page, and delete &rutpdebug=2 again, everything works fine for a while.

Any suggestions?