Users of Plex that used its cloud-based service in order to avoid utilizing an always-on PC or network attached storage unit will soon need to utilize alternatives. On November 30th, 2018, Plex Cloud will no longer be available for existing users.
According to Plex's official frequently asked questions page for its Plex Cloud service, this discontinuation is due to being unable to "...[deliver] a truly first class Plex experience to Plex Cloud users at a reasonable cost."
Also according to the FAQ, Plex Cloud databases cannot be migrated to local Plex installations, with no plans to do so before Cloud's November discontinuation.
Server creation for Plex Cloud has been disabled for all users since February of this year.