Your problem is probably the weight of the encoders on the tracks, they do not press down hard enough. I bought a TL 18 few years ago and had the same happen to me. Sometimes the needle would stay down in the fabric for 5/6 stitches, and it took me nearly 3 yrs to find the cause and fix, both encoders were involved. I bought some mechano-like bits from the hardware store and attached to the back of the carriage, then wedged some styro chunks between that and the tops of the encoders. It has fixed my problem, maybe your DH can figure a better way, I had no-one. Even the shop I bought it from avoided admitting it was happening. I was sent new encoders, but the same applied. Have noticed recently [at the quilt shows] they have a new type of carriage and encoders, so they knew there was a problem.
Hope this helps you, it nearly drove me nuts.