Did you switch back to one of your other threads to make sure the machine is still stitching correctly with them?
100wt is a very fine thread, so my first question would be what size and type of needle are you using? Also, since it is a cone, are you using a thread net over the cone? Without a thread net, the thread may be puddling around the cone or catching on something before it even gets to the tension mechanism of your machine.
To set tension, it helps to set the bobbin tension first then adjust the top tension to match. This video by Jamie Wallen applies to domestic machines as well as longarms:
https://www.youtube.com/watch?v=Q1mRhcquZTM
One last thing. It could be all about how the bobbin is wound. If you did not use a thread net while winding the bobbin, your bobbin thread could be wound unevenly. A problem with how the bobbin is wound will produce the kind of problem you have described.