If you find the coupler bad you should split the lower unit apart & check the lower input shaft. I have seen them twist or snap in two when a stainless prop gets bent on b3s

Ruh...Roh!! That's not good.

The inner prop is solid stainless and I'm sure there is not supposed to be a insert in it.
The outer prop has a small sleeve/insert it it, it has not been spun or damaged.

It's a Bravo 3.

As someone said I may have 2 issues,
one causing the slippage-- coupler
one causing binding-- drive??

I won't have time to put it back in the water for a couple of weeks. I'll do so focused observations then.