There is a problem with the current Android / Android TV app and older versions of Plex Media Server. See the thread linked below for details.
I’m not familiar with Roku devices. Others can assist with those.
PMS 1.18.5 is 18+ months old (released Jan 2020).
If possible, update to the current version of Plex Media Server, 1.24.3.5033.
Download PMS from plex.tv/download and perform a manual installation.
Given the PMS version you are using, you’re probably running DSM 6 on your NAS.
These two documents will assist with updating to the current version:
- Installation & Setup of Plex Media Server on Synology
- Synology FAQ (DSM 5 & 6) - Questions, Answers, and a few How-To’s
Regarding the problem with the Fire TV devices, the thread linked below has the details.
If you do not wish to update your version of Plex Media Server, you can use the workaround of disabling secure communications.
