Ever since we have upgraded our vMix to version 27.0.0.83; This week, on three separate computers, we have experienced that vMix interface freezes and all buttons become unresponsive, I had to use the task manager to close it. It happens even when the computer is freshly started or even with minimal inputs. We didn't have this problem before such as in 27.0.0.81. Is there any way to download previous versions of vmix? I can't seem to find any link for previous version for us to revert to 27.0.0.81.

Please contact support directly to investigate further:

https://www.vmix.com/contact-us.aspx

You can also see here that only small fixes were released in .83 so there must be something else going on specific to those systems:
https://forums.vmix.com/...-27-Changelog#post115166