Dan, I see quite a bit of recovery activity. Neighbor recovery, coverage-hole recovery, much of it by AP "Ind-Exp-2ndFlShipping-AP-58". Anything special about that AP's location?
(Also seeing this type of activity on the 2.4GHz radios as well, but it doesn't appear to be nearly as frequent)
Question: When the 650's were being used, were the handhelds typically using the 2.4GHz radios?
If a survey was done for the deployment of the 650's, was the survey performed based on 2.4GHz coverage requirements? (not for 5GHz coverage)
What I'm getting at here is that the AP placements may have been surveyed based on 2.4GHz coverage...and then you've moved most of your clients over to 5GHz (all of your handhelds). Based on the SmartRF report and all the power recovery activity, I'm thinking that maybe the coverage doesn't look too good using 5GHz.
You could test this by taking 1 or 2 handhelds and re-configuring them to only use 2.4GHz ONLY and then put them into production for a day or two...or however long would prove if the change made a difference. If you see that the connection issues go away on those devices, then I would conclude that you're dealing with a 5GHz coverage problem.