YankeeJim: No, it's not your imagination, I see the same thing periodically. It's part of the cycle where some days you own the game and other days it confounds you.
I concur...but you should notice early on in a round that something is a wee bit different than normal. And YJ is correct...it's all about the pace being a little too fast.
Another one of these oddities is coming up just short on putts that you're so used to hitting that you play them by rote...those days when rote leaves them hanging on the doorstep. They'll make you tilt your head like a confused dog.
I like to think of these things as "close to RL golf" occurrences. Chit happens...you either adjust or curse WGT the entire round. It's better to adjust, eh?