I have a mature system that is very stable, and I have rarely made a change in the last several years! I typically just apply some updates.
Yesterday I upgraded from 2.3.9.177 to 2.4.2.160.
The hub continues to work fine. The apps, rules & devices continue to work fine. BUT!
Every single device I issue a command to via the web interface produces this error (?):
In the above example, I switched the switch on. The switch status changed to ON, the log files (even for devices that allow enhanced debug logging) show no errors, the device physically functions as it should.
A similar error is displayed when changing the device Type; again it appears to be happening with every device:
The device Type is however changed successfully - I only have to refresh the page to see it.
Any ideas?

