Hmm. I think I remember something similar being reported a while back and the issue turning out to be custom mouse drivers. I *think* if you uninstall whatever custom mouse drivers you've got (if any) and go back to using dealt windows ones, that should resolve the problem.
I have same issue, though i had windows default driver with Razer Lachesis mouse. Then i reinstalled Razer drivers, it worked for one boot and then stopped working. While it is probably somehow related to the mouse driver, i think the issue is with the game, not the drivers. I have something like 300-400 different games played with this mouse and drivers and have had no issues with any of them with any given driver.
I remember i had this problem in earlier version years ago, but i can't remember how i got it fixed back then.
It is very weird, it only affects the left button. Right button works fine.
Also, the mouse button does work in settings, it is just in game where it stops working.
