some sources (Sorry for being reddit): 

reddit.com/r/PleX/comments/16iqwf4/anyone_else_get_this_plex_notice/
reddit.com/r/Piracy/comments/16irpgv/plex_is_taking_action_against_hetzner_servers/
reddit.com/r/PleX/comments/16iqyb9/plex_is_going_to_block_servers_on_certain_hosting/

speculation: i can tell you exactly who these people are because they support some major IPTV providers "always available PVR" and it's been going on for probably 4-5 years. people pay for hetzner storage boxes because in terms of raw storage you cant beat the price

genuinely surprised this hasnt happened sooner. it's funny because hetzner is staunch anti piracy and will cancel you at even a wiff of a DMCA in the wind

wondering when ISPs will do the same for hetzners disregard for abuse emails about botnets that have existed on the network for over 5 years or if they are subsidized by hetzner to give trannies somewhere to reload