Lots of reasons why it's happening. Is your bobbin in its holder correctly, clockwise or counter clockwise.....was your bobbin wound correctly, is your thread in the bobbin and top the same weight? ie: 40 wt in each or 30 wt or 50 wt, etc.
In my Gammil is the needle is off center just slightly it makes a huge difference, also needles are not inspected and can not be perfect out of the box.
Do you have a fuzz ball somewhere in your bobbin area that is interfering??? If all else fails: but your thread from where you cone of top thread is, remove through the needle and RETHREAD, don't just tie on and drag your thread thru.
Slow down, breath, and eat a piece of chocolate.