I would like to report a similar issue: Plex stops playing after 1 second or does not event start at all. Here is my environment: Synology DS218; DSM 6.2.1-23824 Update 4; ethernet connection; Windows 10 Pro. I’d like to add that it has been working properly until a certain moment.
I might have been a bit unclear – sorry. It does work perfectly fine when I launch Plex via www.plex.tv and enter my username and password. However, the problem occurs when I launch the Plex app for Windows. I am attaching the diagnostics file which is created via the app.