I have a similar situation, very odd, with Add to Cart (AtC). I have two sites running the RC-J. One has been hacked on a bit, , and was upgraded from 1.5, I believe, but I see that when I scroll the "neighbors" at the top of the product area, the AtC is there, EXCEPT for the first and last items in the series, which lose the AtC and the neighbors arrows...But only for one category not another, corporate/gifts does not have the issue, but healthcare/hospitals with about 5 products does, and drinkware/travel-mugs with one product.
On the FRESH RC-J install, there are no such issues and both 2-product categories and multi-product categories shot the AtC.
I haven't tried what the OP has, but can empathize, as this has plagued me for a few hours now.