Hello,

I am currently testing redundancy using two UC20-M4000 controllers with CODESYS Control SL.
The basic redundancy functionality (Active/Passive switching and failover) works, but I am experiencing problems when updating the application.

Environment

Controller: Weidmüller UC20-M4000

OS: u-OS

Runtime: CODESYS Control SL 4.12.1.0-1

Redundancy link: dedicated Ethernet connection between the two controllers

Time synchronization: NTP configured, time difference between controllers is about 1–2 seconds

Current behavior

Application synchronization
When I download a modified application to PLC1 (Active controller), the application is not automatically copied to PLC2 (Passive controller).
However, when I perform a path swap, the application download to PLC2 starts automatically.

My expectation was that the Passive controller would automatically receive the updated application after downloading to the Active controller.

Online change
When performing an online change, redundancy is lost and the controllers switch to Standalone mode.

Typical log messages include:

RedundancySynchronize called

Redundancy failover itself works correctly.

The application boot project exists on both controllers (Application.app and Application.crc).

Network interfaces are up and correctly configured.

Question

Is this behavior expected when updating the application in a redundant UC20-M4000 setup?
Should the Passive PLC automatically receive the updated application, or is manual synchronization required?

Any advice or recommended configuration for stable redundancy during online change and application download would be greatly appreciated.

Thank you.