Server Version#: 1.15.3.876
Player Version#: 3.83.1
The NAS is prompting for an update to server version 1.7.2.3878 (dated May 26, 2017).
Following events are generated on your MyCloudPR2100 MediaServer.
Event title:App Update Available
Event description:plexmediaserver app has update available. Please update.
Severity:warning
Event code:1501
Event time:04-18-2019 04:00:04 AM
Firmware version: 2.31.174
This email prompt to update has only recently started to occur, and i normally update the NAS manually.
I tried updating to the old version - the alert message disappeared on the NAS - but of course Plex itself prompted for an update to the latest version. As soon as that was installed manually the NAS alert message reappeared.
TL;DR version - Plex changed the numbering format, so newer versions are now recognized as older by WD dashboard. Get used to it, as Plex does not care.