I need some HELP!

I thought I'd sorted it.
What? you might ask.
My overlocker tension, that's what.
I used a you tube guide to sort my tensions - all was fine, working well. Then I changed the threads!
At first I thought it was the thread I was using - so I changed back. Same fabric now with rubbish tension.

Actually I think it's just one thread. My left needle thread. the rest seem to be ok.  The left needle tension is too loose. It doesn't seem to make any difference what setting I put the dial on it's still too loose.

Someone out there must have a clue as to what the problem could be. I would really appreciate it if you are able to help me sort this problem.

Thanks

Claire