Same thing happening to me, though it did happen once before in 1.5.2 patch (0 times before that). How I got it to replicate is I turned on instant replay (nvidia feature) and after turning instant replay off after some time (maybe ~2 minutes), Alt1 would crash and come up with an error report showing cpu capabilities then something about win32. Then giving me the only option to exit Alt1 toolkit. From there, anytime I click on the client the windows sound would play and like you said, render the client unable to receive any clicks or keystrokes. The replication step does not always work but its the only thing I found to make this instance repeatable.
Specs:
Ryzen 7 1800x
Geforce 1080ti
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