Sounds like maybe your spring for the tension is not working properly. All it does is help to keep the thread a bit snugger around the needle as the uptake lever is going up to pull the thread back up from from the hook going around the bobbin thread.
I had this happen with my Long Arm. There was some lint and once in a while that spring would not spring back like it should and that caused enough looseness in the thread as the needle was going up and down that the thread would wrap around the needle. And since I was going over seams regularly, it was breaking often so I was motivated to get it figured out and started watching carefully.