What kind of spool of thread? Stacked thread likes to be upright and cross wound like to be sidewise to feed properly. If you are using a thread stand behind the machine, make sure the thread isn’t catching on the way to the machine. Older cotton threads break easier but if it is polyester, those usually don’t degrade like cotton threads.
If you are using a single hole plate, try switching to the zig zag plate. Sometimes pulling on the fabric will move the needle a little off center as it goes through a single hole plate and it will cut the thread.