Alrighty, this looks like known MQTT 2.4 binding misbehaviour.
It’s all a bit bizarre; setting UNDEF once would be a reasonable thing to do at startup, while awaiting first topic publish. But not continuing to force it.
This looks to be a fix
If you prefer not to go to snapshot binding version, review why you would want to restore-on-startup Items that you are expecting to update every 10 secs anyway?
