ok i might know what it is.
your kinetic chain is sometimes broken. on some shots your shoulder looks ok like on 1:32 and a couple of others. in those shots you can see that your hips are firing before your shoulders. Then your shoulders have more power. on other shots you rotate your shoulders before your hips or at the same time..., a little more 'arming' going on. not too bad though. Then your shoulders are 'done' before contact is made. Maybe this has to do with you not using your legs enough. most of your shots are hit off the front leg and there is no push off the ground. Maybe if you try to get some more shots from off your back leg it could help.
also on most of your shots your shoulders are turned at the same angle as your hips at the end of takeback. they need to be turned more than the hips to create torque. you are rotating your hips and shoulders as one unit. they should be separate units. like a coiled spring. hips first then shoulders.
this is called separation.
look at the monfils vid above. you can clearly see his shoulders are turned back much more than his hips and then his hips clearly fire first before the shoulders.