A size 18 is the correct size needle to use with King Tut. Go here and download the "Longarm Machine Thread Reference Guide"
http://www.superiorthreads.com/reference-guides/ Hang it up near your LA machine and use it. Remember it is the thread you use that dictates what needle size to use.
Have you tried changing the needle? Did you completely rethread the top? A top thread break can cause the thread path to jump out of whack, had that happen to me once, it double wrapped around the needle take up. Also you may wish to try slowing down. New LAQ who do a loopy design like you pictured tend to go way too fast and then slow down to complete the loop. These drastic changes in speed causes backlash to happen in the bobbin. The bobbin is spinning inside the bobbin case and it causes these loops/skipped stitches to happen. You can switch to magna glide bobbins which help backlash issuses. But, more importantly, you need to try to regulate your speed so you are going a more even speed without the drastic slowdowns and speed ups. Yes your stitch regulator is keeping up with you but the bobbin isn't. This isn't a race so try slowing down a bit.