I think JB has been on the heavy side since before his injury. It didn't affect him before his injury and I think that's part of what gives him his huge power with the bat.
I think the strain of "squatting" for long periods behind the stumps after a big injury must be difficult.
Apparently his batting average dips on a 2nd innings...maybe due to fatigue of wicket keeping. He doesn't appear to be IMO the most nimble because of his size.
If he was batting anywhere near like he was last summer nobody would be mentioning dropped catches or missed stumpings.