I've got the same one

How long since you've changed the needles? They should be changed after 10 hours of sewing time.

Unthread it, blow out all the fluff and rethread it with all the tension set to neutral (4 or 5 can't remember off the top of my head).

Set your diff feed to about 2.5.

Try sewing on some scrap fabric, reasonably thin such as flanelette to check it's working alright and the loopers are meeting in the middle.

Failing that how are you applying pressure? I find mine can skip a thread if I go a bit quick then back off.