I as having the same problem, same reason.

Thanks for all of the advice. The thread is the same weight in both top and bottom. I was told to never play with the bobbin tension from the dealer. I think I will try adjusting the top tension and see if this will help. I forgot that I did change the top tension a few weeks ago, maybe I forgot to put it back. Usually I don't touch my tension at all for fear of messing it up. I also thought my speed could be off, but no matter how fast or slow I go it still messes up. I won't get a chance to play with it again until the end of the week. So I will let you all know what happens. Thank you.

Try using different types of thread on a practice sandwich. I ended up buying Isacord...online. and that helped a bunch. It is a poly thread I believe...some machines prefer one brand or type of thread...go figure. Mine prefers cotton thread or the Isacord. I ended up buying a machine that only does straight stitching and that ended my bobbin problems. My stitching improved a thousand per cent after months of practicing FMQ. Juki solved my probs.

Are you pulling your bobbin thread to the top before you begin stitching, and make sure your presser foot is down... the times I've had a nest on the bottom was because I'd forgotten to do either one or both of those two things....