I too had problems when I added a receiver end plate sling adapter.
I used the ERGO ambi sling plate, also about 1/4" thick. I used mine with the Hogue short LOP which uses the factory stock bolt, but still had to do like wise and go to the hardware store for a longer bolt to use the sling plate.
Using the sling plate introduced another issue however. Well, a couple issues, one compounded by the other. You know the lug on the bottom of the receiver that sticks out to mate up with the notch in the stock? When you add the sling plate, this lug thingy becomes useless and no longer mates to the stock at all, which introduces the first problem. Stock twist. I know not everyone experiences the stock twist, but it was a problem for me. The stock would rotate on the bolt axis, so I fgured it simply needed to be tightened. This is where the second problem begins. The receiver of the 590A1 is an aluminum alloy and softer than the steel bolt, so over tightening could result in stripping the threads out of the receiver. (Parenthetically speaking here, Remington has a clear advantage having an all steel receiver).
I never could (safely) tighten my stock bolt so it wouldn't rotate. I would get it very very snug, to the point I felt anymore may very well strip it out. It was tight, but I could still feel the give in the threads and I wasn't willing to risk any more. If it were steel, you could torque it down pretty hard and it would crush plastic in the stock before damaging threads.
While I liked the ERGO plate, I removed it in the long run for the reasons listed above. I decided on the Specter Gear sling and stock adapter if I would want a sling on it.