Sure they fluctuate. Baseball is a highly random sport. Nonetheless, there is some year to year correlation. The year to year correlation for OPS is roughly .6, a moderate positive correlation.
Here is a scatterplot of year to year batting clutch data, and Jeff Sullivan's interpretation of it. That picture pretty much says it all.
There’s next to nothing there. If there were absolutely no relationship, we’d expect an R2 of 0.00. Instead, we get 0.01, with a best-fit line that has a very, very slightly positive slope. If you wanted to be extremely generous, you could say that batting Clutch has a slight tendency to repeat. Truthfully, though, this is a scatter. There’s no meaningful signal to be observed.
https://blogs.fangraphs.com/the-most-important-thing-about-clutch/