I wonder if it's his shot quality that has fallen away? He's been getting plenty on goal but maybe they are just not very accurate and goalies are finding them easy to stop?
There is also some data around his shot having lost a few mph, which would definitely make that PP one timer easier for goalies to stop.
I pulled the most recent data. His shot speed (max, average, over 90 mph) are all in the top 1-10% of the league. It doesn't need to be 90 mph to go in, but he's still launching them.
To me, the passes come to him a bit slower than they used to, so the goaltenders have more time to prepare for them.
Carlson and Backstrom use to rifle passes for one timers, but Ovi doesn't seem to be able to connect on those anymore.