Hi Yanni,
This is my first time on any forum but for what it is worth i think Eric is most correct Spongy spots and hard spots will often cause this problem, but further a new needle will often solve it. The tip can have a very slight twist and deflect sideways away from the hook. Next the hole in the needle plate should not be too enlarged out as this allows the softer leather to go in and hold the thread elastically against the needle and miss the hook. The gap on the foot being too large will create the same problem. Check carefully for any catching on the thread return spring and polish up any bits if needed. Last try lifting the foot by hand upward and if it feels grabby work out why and fix. Silicon spray if you must.
Best of luck Brian
