it a wound or prewound bobbin if it is wound by your machine try winding it again umm blow hard in the bobbin area sometimes dust does that rethread machine some things i can think of tension set right bobin tention set right?

Check your bobbin casing to see if there is alot of lint, try re threading both thread and bobbin, check tention.

I don't know the make of the machine you have. I have Husqvarna and the bobbin casing has 2 screws on the side, a big one and a small one. I adjust the bigger screw a little bit every time I have to change threat thickness. When I give the threat a little tug it must come out of the casing gently, not to easy and not to tight, tight makes my top thread snap, and to loose give me the problem you have. Hope it helps.

my machine is Janome 350e and if the bobbin thread shows i just adjust the tension from 2 which is ok on all my designs to 1.5 to 1. this usually works especially if i am using metalic thread. you can phone your dealer for help they usually tell you the problem.