Automatic buttonhole problems on a Brother

[TractorComesFirst]

Help! Before I throw my stupid sewing machine out the window.

I am trying to do an automatic buttonhole on my machine. I managed to do 3/4 practice one evening perfectly and then when I went back to it again another evening it now won't sew them properly at all. It won't sew the front tack at all and sometimes gets stuck on the back tack. Has anyone else had this problem?

Bobbin in correctly? (I've made this mistake a few times). Tension correct? Correct needle for weight of fabric & thread - I didn't know this matters. The handbook should guide you.

Thanks, I have been through all those checks and It's still not working. I have just switched it back to normal stitching and although it's doing it the machine is making a funny noise so I'm going to take it for a service.