Fighter class feature says
You adopt a particular style of fighting as your specialty. Choose one of the following options. You can't take a Fighting Style option more than once, even if you later get to choose again.
Paladin class feature says
Fighting Style- Starting at 2nd level, you adopt a particular style of fighting as your specialty. Choose one of the following options. You can't take a Fighting Style option more than once, even if you later get to choose again.
So this leaves me wondering; Paladin and Fighter both gain this feature as class abilities, with the restriction that if you later choose again you can't take an option more than once.
For purposes of Game Terms, are they both "Fighting Style: Defense" and unstackable, or are they each "Fighter Class Feature: Fighting Style: Defense" and "Paladin Class Feature: Fighting Style: Defense" and able to be doubled up at 1Fighter/2Paladin?
If you went 10Fighter(Champion), you would gain a second Fighter Fighting Style (which has distinctly different options from the Paladin Fighting Styles), and for sure not be able to take Defense twice, but since they're from separate classes, I'm uncertain.