Counter-Strike: Global Offensive to be 64bit, so if you're still stuck in the past it's seriously time to upgrade. Valve say this fixes numerous long standing random crashes.
It seems the new update has introduced a host of new problems, with people reporting reduced performance in general, framerate drops they didn't have before and more.
I tested a round myself earlier and the framerate does fluctuate rather a lot.
If you do have issues, be sure to report them on github.
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