Disabling the network, or disconnecting the Ethernet cable, and/or turning off Wi-Fi is a good idea, but a script may still be run by the browser and cause the problem, regardless of internet connectivity.
I would have thought that the name of the script would be in the error message that pops up, somewhere. If you see it again, see if you can work out which script is running.
You haven't set Edge, the new Microsoft browser, as your default browser have you? That could definitely cause issues, since from what I have heard it lacks a lot of features just yet, such as running scripts. You should be using either Internet Explorer or Chrome as your default browser, and the Browser Engine in MC. (Options/Tree& View/Web Browser/Engine)
Try disabling ALL add-ins in the browser, rebooting, and then try MC again.
If that works, then re-enable add-ins one at a time until MC stops working again. Maybe you will even be able to see an add-in that you don't think should be there, which could have been added recently without you being aware.
If none of that works, try starting up the Windows Resource Monitor before starting MC, with the CPU usage page open, sorted by % use, then open MC and watch what is using the CPU, particularly as MC fails.
Let us know how you go.