Please please someone help!
I have been doing a load of sewing and my overlocker was working fine and then it started playing up. It misses a thread in its stitching, but sometimes includes it.
I have looked at the threading and cannot see anything not in the right place, so I dont know why this is happening. I think the tension is the same with all 4 threads...its very fustrating and wasting my time and making a mess of my sewing.

I do not have the owners manual and have looked online to try find something for helping but cant find anything, so hoping some clever person here can help me.

Its a Bernina 700D