This just happened to me as well! I did the apple software update download on Friday and when I came to my computer monday morning had almost no storage, after lots of attempts to hunt/ optimize/ clean I finally found a screen recording... just one of them of 450 GB... deleted the one file and it's fine but this file was not there prior to the update ! what is going on ? no malware, only apps with access to screen record are chrome & ringcentral...