The Realtek RTD1296 is ARMv8. See NAS Compatibility List.
Did you update from DSM 6 or DSM 7?
If DSM 7: FAQ 34: Upgrading Plex to DSM 7.2.2+
If DSM 6: FAQ 27 - Migrating an existing PMS from DSM 6 to DSM 7
The Realtek RTD1296 is ARMv8. See NAS Compatibility List.
Did you update from DSM 6 or DSM 7?
If DSM 7: FAQ 34: Upgrading Plex to DSM 7.2.2+
If DSM 6: FAQ 27 - Migrating an existing PMS from DSM 6 to DSM 7