Good ideas will try unplugging kb and mouse next time it does it. My other older machine doesn't do it so have changed the lock screen settings to slideshow of wallpapers from picture of the day/Bing that is the only thing different on the two machines. Like all good annoying bugs it is totally random.
What is annoying with a hard reset it corrupts my NTFS partitions so have to boot windows to run chkdsk to fix them or they wont mount in Solus.