Thanks abdullah.
The problem is fixed, although I’m not entirely sure what the cure was.
This morning I connected the ezcan to the Accessory Manager updater software, and it advised me my ezcan is a “RELEASE” version and needed to be updated with the “RELEASE” version of the software, which I did. I updated the ezcan only two days ago, in an unsuccessful attempt to fix the problem with the K2, but that update made no mention of “RELEASE”. I’ve no idea what “RELEASE” version means. Can anyone help me with that?
Unfortunately the “RELEASE” version did not fix the problem with the K2. Then I found the button in the Accessory Manager that allows an unused Anccessory channel to be switched off completely. I toggled the channel powering the K2 off and then back on again, and my problem was fixed! The K2 is now working normally powered from the ezcan.
My guess is that somehow the thin signal wire from the ezcan has been switched off somehow and it came back on when the ezcan Accessory channel was cycled.
[UPDATE: Hex have advised me that by “RELEASE” they mean the version ready for general release, as opposed to “BETA” for example, which is a version still undergoing final testing. I have never seen any of the previous updates to my Ezcan named in the update window as the “RELEASE” version. Still, that particular mystery is now solved.]