I have the same issue with skipping stitches. Since I bought the machine almost a year ago, I've had constant problems. I have become adept at changing and testing the timing and needle position because that's what the technician (when I called and we video chatted) taught me to do. (As a side note, I can't believe that they don't give you better insight online how to do this - they just give a measurement of how far the needle post needs to be and if it's off by 0.1 mm then you're screwed. They could have had an instructional video to show people where it needs to be when it hits the bobbin.) Anyway, that TechSew service guy was grouchy and condescending, and would say things like "make a video of yourself threading the machine and then send that to me and then I'll talk to you". When he finally saw this issue about the needle timing, he told us the logical way how to do it (when I say 'us' I include my husband who could also not figure it out, and we both are PhD engineers who are quite good at all things mechanical!).
Anyway, if anyone can help, we have checked timing, needle size, new needles, etc, and the machine skips a stitch about every 3rd stitch. I cannot find anything helpful online about this. I have resorted to my $200 Singer Heavy Duty machine for lighter leather projects because it's reliable.