Video takes a long time to load.
PMS transcodes the video into 4MB chunk sizes. The lower the quality, the longer it takes to fill up this chunk, before it is played on the client device, on devices which uses matroska container instead of HLS container.
Tested with i5-3570K Quad Core, 32GB RAM, SSD, Windows 10, PMS 1.1.4
Increase the Plex video quality on the client. Typically: Settings->Player->Online Quality
Change Plex Client Settings->Video->Transcode Format->HLS
Noticing the same behavior... would like to improve the signal acquisition time on the Roku Premium+. When viewing an OTA channel via this plugin using the Plex Web app (1.2 beta 4 for DVR), signal acquired within a few seconds. However, best I can do on the Roku Premium+ is 45s.