Maybe it’s time to talk about bobbins and how deftly they can mess with your machine.
First off, all you top loaders:
Is there a bit of thread caught in the tension spring in your bobbin case? If there is, bobbin tension will be way too light, and your machine will sew very badly. The fix is easy...tear the corner off a stiff piece of paper, like an index card, and push it between the tension spring and the side of the bobbin case to dislodge the thread. That usually does it. More commonly: is your bobbin in upside down? This particular gremlin applies to both top loaders and side loaders, and will indiscriminately attack any of us with no warning!
What should it look like?
If you have a top loader, the bobbin drops in to the bobbin case from the top, with the bobbin case trapped in the machine. The thread should come off the left side of the bobbin when you pull it towards you. That action should rotate the bobbin counter-clockwise.
If you have a side loader, you will have the bobbin case in your hand when you insert the bobbin, and you will be looking at the back side of the bobbin case.
In that situation, the thread should come off the right side of the bobbin when you pull it towards you. The bobbin should rotate clockwise.
OK….I know all of you have threaded about a million bobbins in your sewing lifetimes, but sometimes the simple things we do every day get messed up for no apparent reason. We see these problems often enough at the shop to make the reminder viable. You shouldn’t have to bring your machine in for something like this, when you could be sewing, even though we enjoy your company and would like to see you!