Several times when I get close to the bottom of the thread I noticed the thread is curley and messes up my sewing. I use to buy cheaper thread and now I buy the better thread and have no problems.

So often just taking the thread off and then rethreading helps me so much. It is one of my first go to steps.

Check to make sure bobbin is wound correctly and evenly. Are you using the same thread on both botton and top? or at least same kind such as both cotton or poly. Check to make sure bobbin is threaded correctly. Sometime mine comes unthreaded. Do not use cheap or old thread. There hase been several messages about thread drying out.

I had that happen to me for a while and then I figured out that when I thread my machine that I need to just give a little 'tug' on the thread after looping it over that uptake bar and it straightened itself out. It happens to me on my new Pfaff Quilt Expression 4.0. I don't know if that is your problem but it is worth a try. Just re-thread it and give it a tug.

Most likely your bobbin thread has gotten too loose by the screw vibrating out a bit, or there may be some lint in the bobbin tension plate that prevents it from putting any tension on the thread at all. Make sure it's clean behind the bobbin tension plate (on the bobbin case) and then put another bobbin in. Test the tension by holding the bobbin and case by just the thread. You should have to shake the thread lightly to get the bobbin to unwind and drop down. If it just drops straight down as soon as you let go of it, there is not enough tension. Tighten up the tension screw a little at a time and keep testing, until it's tight enough that you have to shake the thread a bit to get the bobbin and case to drop down.

Change the needle for a new one and make sure the flat part of it is facing away from you when you insert it. If that fails, check for lint or thread in the bobbin race and feed dogs and adjust your tension.

I had the same problem the thread wasn't right for the needle and the cloth... bought new thread and no problemsssss

Yikes, I hope you get it figured out. I hate when something like this happens.

i agree with all of the above !!!
i had a problem once like yours and for some reason my bobbin was not wound correctly

I had this same problem and went through all the mentioned proceedures.....discovered I had placed the spool of thread on backwards for this machine.