If mine starts skipping stitches I use sewers aid. I got very flustrated with my BSR one day and finally tried it. I had tried everything else I could think of to try. I put about three lines of it on the thread and also on the bobbin
thread. It has so far fixed the problem. The sewers aid is a thread conditioner I had bought years ago when having the problem a machine. Joanns has it in the notions section.