As posted above. It is the seats in front of exit rows that do not recline.

For the OP I had that happen once before, the result was the same with the FA getting involved but played out differently. Boarded right after two people who were sitting right in front of me. I cannot recall exact circumstances or the exchange but they were overhead bin hogs and I used another bin. Then not long after that a bag appeared by my feet. I pulled the bag out and pressed the call button. When the FA arrived I said someone from the previous flight left their bag on board in the under seat storage and could they give it to the GA. As I handed it over the overhead bin hog PAX notice it said it belonged to them. The FA instructed them on the proper under seat storage etiquette and rearranged the overhead bin so additional bas could fit in.

I should add even when in such an exit seat with unlimited foot room I do recline as fully upright seats are uncomfortable for me.