Score suddenly speeding up and slowing down right before tempo changes

Hello,
I've been working on a score that has numerous tempo changes in it. I'm wanting to get an audio file with a metronome to my drummer, so I added a click track via a woodblock.
Now for some reason, the piece will suddenly speed up or slow down the measure before the tempo change.
Strangely enough, I even went back to an older file that I'd saved as a backup, and it is doing the same thing now, even without the woodblock track!

What could be causing this?

Thanks so much...

Matt