Not here to bash but to actually try to help make Avast better. Long time user and it has saved me enough to know it can work.
I wish I could supply more detailed information, but I had to restore the windows 10 machine that was wrecked from a disk image, I could not boot to it again. So I cannot supply you with lists of files or logs.
Fortunately I know exactly what did it…
I had just installed the cygwin64 X server and was running it for the first time. It came up, and got stuck. I went to start a mintty shell, and the mintty executable had been deleted. I found a whole bunch of cygwin64 executables had been deleted. I didn’t know it at the time, but so had a bunch of Windows 10 files. I eventually tired to restart, and could not get that windows install going again. Recovery console was no help.
When I reimaged, I installed cygwin64 again without the X server. This time I just ran ssh.exe (with the -L option to tunnel a port) and Avast went and deleted a whole bunch of cygwin64 executables again, including ssh.exe and mintty.exe. It only mentioned ssh.exe in the quarantine, though, despite deleting many more. This time it did not kill windows, thankfully. I disabled the behavior shield, reinstalled cygwin64, and now everything is fine.
I suggest an assessment of behavior shield. I added my Cygwin directory to execptions but I am going to run with it disabled for a good long while to be safe.