It is still looping under the fabric, then jams

It's still not threaded correctly!

I think you may have the thread laying 'on top' of the tension discs, (hence whatever number the tension is set at wont make any difference) the thread must be pulled or tugged a little to make it pop between the tension discs.

When threading always thread with the presser foot in the up position, which opens up the tension discs to allow the thread to locate to the correct position.

Keep the thread taught while threading the machine.