Question about training new position

So, i trained one of my strikers to be an an accomplished AMR, and then i kept training him to that position for more one or two weeks. After that, i started training him to the MR position, cause' that's where he plays, he went from Akward to Competent, but after he became a competent MR, his AMR positiong felt and he became only competent there.

So my question is, did that happen because i wasn't playing him at the AMR position or was it because when he became a competent MR, his AMR positioning rating dropped due to low versatily or something like that?

...So my question is, did that happen because i wasn't playing him at the AMR position or was it because when he became a competent MR, his AMR positioning rating dropped due to low versatily or something like that?

Partly yes, and yes. Both, but mostly versatility...

Edit: You should have skipped AMR altogether, BTW. I understand (I think I understand, anyway...) that you were tyring to transition him from ST to MR, but he'll improve more as a ST if you train and play him as an MR...

Following up: Is a natural AMR/L automatically (or most-likely) adept as MR/L? I've seen players having AMR/L as their natural position yet they play as MR/L for the club in a 4-4-2 formation. Cristiano Ronaldo and Lionel Messi as prime example. Should they still be retrained further as ML/R to improve their effectiness as an ML/R? Or you can't go any futher once they're Accomplished?

I've never seen it happen, but I have heard people say that if you train and play a guy in a position then he can become natural there, but it takes a while and he needs to have a good versatility as well. Most players who are natural AMR/L can be effective MR/L even if they are not accomplished there (most are however)