Model distorts/stretches when placed on the controller?

First of all, I'm still new and getting used to unity, so the way I've used the FPS controller is a bit different. I usually take the camera out of the FPS controller in the hierarchy and then put the player model in it's place and drag and drop the camera onto the model once I'm happy with the view of the camera.

Now the issue I've encountered is I'm trying to set it up so by pressing a button, you can switch between two character models to play as. Unfortunately this is where I found the issue.

The first player model and camera is set up fine, all working nicely but with the second model, I did the same routine of putting the model in the FPS controller only this time, it distorted the model in such a way that it's been stretched out thin and angular and even after struggling to reshape it, with a slight movement, it stretches out again and I know this isn't the first time I've encountered this issue.

I read somewhere(while googling for an answer to this issue) that someone had "stretched" the model graphically with their camera(they had also used FPS but attached a pair of arms to theirs and suffered the same stretching issue) However I do not know how to access or check to stop the FPS controller from stretching out the second player model.

Now I'm not worried about the character/player switch, I just want to know how to stop the FPS from stretching/distorting my model.

If this is in the wrong spot/category/forum I apologise but I'm seriously stuck on this issue :(