Funny, I just started having the same problem!  It started when I put on the walking foot, which I haven’t used in ages.  The only way I could solve it was to take the foot off and put it back on again.  Not sure if it was from the S9 or 15000, since I have 2 black accessory cases.  I purchased one for my 12000, and the dealer told me to keep it when I traded it.  Of course, it came with the 15000, so I put the feet for the S 9 in the extra one.  The feet are interchangeable, so could that make a difference?  Also, I’m now having trouble with the needle threader.  Had it replaced as part of the update, and it worked fine until recently .  My dealer tried it 5 times successfully before he let me take it home.  Tried different brands of thread and it didn’t seem to matter.  Now I try it once, and then thread by hand!  Any suggestions?  Thanks.