If this happens on more than one new magazine, it is most likely your grip. If it seems confined to one magazine, MIGHT be the magazine.
My best friend has the same issue when he shoots my P226. I do not have this issue, as my thumbs are shorter, and my hands smaller overall.
Worst case, have someone else run the gun to find out for sure.
VIGILIA PRETIUM LIBERTATIS
"The price of liberty is vigilance"
America is at an awkward stage. It's too late to work within the system, but too early to shoot the bastards.