Sounds to me that you overcooked your turkey.
What internal temperatures are you taking the breast and thighs too?
Also from what you are saying you basically took it off the smoker, added butter, then wrapped and put it into the cooler. You didn't vent your bird, so it held onto the heat in the foil and kept cooking while in the cooler. If you are waiting 30mins to carve it up, don't worry about the cooler. Just keep it on the counter, with a loose tent of foil. This will allow the heat to escape and keep your bird from carrying over cooking too far.
*Weber Mini WSM* *Weber Touch and Go Performer X3* *Sublime Smoke UDS* *Maverick ET-732 * World's Fastest Blue Thermapen **Pitmaster IQ110*