Could be machine threading – Make sure your machine is threaded properly according to the manufacturer of your machine. Also be sure the presser foot is UP when you thread – otherwise the thread might not “catch” in the tension disk properly.
Could also be that tension needs to be adjusted for this project, increase upper thread tension (internet search your machine and tension to find answers on the web)
If you still have issues, you may need a thread hack to avoid loops on the thread path. See my post on Get Rid of Thread Nests for Good.
Your top thread tension is too tight, causing the bobbin thread to be pulled onto the top of the fabric. Most often this is caused by improper threading – check your manual. Or your thread might be caught on something and not flowing properly. Watch the machine stitch to see if this is the case. Be sure your thread is not running through the bobbin tension disk or wrapped around a machine part where it doesn’t belong. (we’ve all done it!)
If you’re sure the machine is threaded properly, you can decrease the tension of the top thread to see if that helps.