I suspect you have some settings saved that are no good with the current client. Let’s try deleting them. First, quit the game.
Look for your Steam install folder. We want the folder for Steam itself, not necessarily where Evolve is installed. Inside that is a “userdata” folder. On my computer, it’s at “C:\Program Files (x86)\Steam\userdata”.
Inside that will be (hopefully) one folder with a name that’s all numbers. It corresponds to your Steam ID. Go in there.
Next, look for a folder named “273350”. Inside that, “local\USER\Profiles\default”. There, there should be a settings.xml file.
The whole path on my computer (with my Steam ID redacted) is:
C:\Program Files (x86)\Steam\userdata\xxxxxxxx\273350\local\USER\Profiles\default\settings.xml
Delete that file (or, if you feel safer, just rename it to settings.bak).
Next, find your user folder – the same one that contains Downloads, Documents, Pictures, etc. Look for this file:
Delete or rename as before.
Run the game, and see if that fixes it.
Edit: An alternate technique is simply to delete the entire contents of the 273350 folder. This is more thorough about wiping old data. However, it will delete any cached shaders built locally. If you have suffered from the stuttering caused by missing shaders in the current build, think twice before deleting everything.