There could be several reasons why the upper thread keeps breaking.
+ The area around the hole in the needle plate is damaged.
+ The needle hits/touches the needle plate.
+ The presser foot is set too high and not correctly positioned. The needle hits/touches the presser foot.
+ The area around the embroidery foot hole is damaged.
+ Sliding surface on hook race is not smooth.
There are scratches or burrs on it.
+ The play between the hook and the race is too much.
+ The space between the hook stopper and the hook cannot be adjusted.
+ The automatic needle-threading mechanism is broken.