hi check all your connections and your encoder connections to make sure thee is no lint around the wheels. then check your connections if you have a stitch regulator.
From what I understand that there are several reasons that you could be skipping stitches: needle needs to be replaced (check that it is in there correctly), the upper tension is too tight, the wrong size needle is being used for the fabric, the needle in hole in the throat plate is too large, and finally the threads may not match in the bobbin with the upper thread. T
the other day this happened to me and I discovered that there was a piece of thread that had escaped the bobbin when I had wound it and it interfered with the sewing stitch. Consequently I got tangles and skipped stitches until I got that bit out of there!