Generally speaking, it depends on just how identical the faces are for whether I deem it a problem or not. Even if an author uses the same face/jaw shape a lot, oftentimes there's enough differentiation in the way eyes, nose, etc. are rendered that make them stand out at least a little bit. That I don't mind so much.
What I do mind is where it's like uncanny valley status copy/paste faces everywhere xD like if everything except the hair (or even including the hair in some cases) are drawn almost exactly the same with every character it's a little ehhh for me. I still read some comics like that (it's not a huge turn off) but yeah.
I had a little bit of SFS myself in the past (mostly just using the same face/jaw shape for almost every character) so going into my current comic I decided to at least make the 3 main characters each have different face shapes, just to practice using different ones xD some of the minor chars have repeat shapes, but I've tried using some variety there too

(Square, round, triangular)