I have trouble dealing with very slow and extremely spinny loops. when I  smash the ball it often goes long and outside of the table. what am I doing wrong?

Try closing the bat a bit so the ball goes lower.

dont smash it, reloop it with some spin of your own, or block with a closed bat angle.
Smashing is completely devoid of any touch/feeling, which is the worst thing imaginable against spinny loops.

It requires some touch.  Try to play with that player more often.  I remember seeing a few clips of Timo retrieving a net/edge ball by loop it from way under the table with tons of spin.  His opponent (Ma Long, ...) then blown the slow spiny ball.  So even the pros having problem handling such balls.

the key is to be gentle with the ball, not rough...
sensitivity.....

alexmori wrote:  I have trouble dealing with very slow and extremely spinny loops. when I  smash the ball it often goes long and outside of the table. what am I doing wrong?

I see you use Flarestorm... The technique is called "carry over" in Chinese.  You'd want to "guide" the ball over the net to the spot you want it to land by maximizing your contact time... The key is to use minimum backswing when you block or hit the ball, and try to feel the ball with your rubber only, not with the blade at all.  Precision is crucial:  You must look at your contact and make sure you are not "impacting" the ball with your stroke, but rather "catching" it with your rubber with perfect timing and guide it over.  Once you have perfected this "catching" technique, you can then add pace to the stroke and actually start to smash such spinny balls with your pips.