I realize the common date makes it suspicious, but for the life of me I can't think of any reason an external device could cause a Windows crash. And by external I mean not connected to the computer in any way other than a network protocol. The external device (in this case a Roku player) has no connection at all to the Windows OS. All the player does is request the Plex server to stream the media to the player. There's just no way I can fathom that there could be something in the Roku OS that causes a Windows OS failure. Now if there were a Plex server update around the same time, perhaps that could be the issue. But nothing an external device can touch can cause a BSOD. In general, the Blue Screen is caused by either a driver misbehaving or some sort of hardware problem with the motherboard or its attached components (RAM or CPU). I have Plex on two computers (Windows 7 and 10), and have Roku devices connected to both. I haven't seen a blue screen in years, and that was a RAM issue.
If possible, try stopping Plex for a few days and access your media via Windows Media Services, or try a free DLNA server. If you no longer have Windows problems, then it seems clear it's a Plex server issue.
Nvidia Shield, Roku Stick (3600), Ultra (4640), Premiere (3920), Insignia 720p Roku TV, Sharp 4K Roku TV, Windows 10 Pro x64 running Serviio and Plex on a wired Gigabit network.