There definitely is a difference given the events.log. There is no GroupItemsChangedEvent for UNDEF which means there’s no event to trigger the rule. I don’t know if that’s a deliberate choice or not but suspect this behavior only exists for Group Items.
It used to be the case that you could not update a Group Item at all. I don’t know when that changed, but it very well could have changed after OH 3.4.
If there is a bug here, a fix certainly will not be back ported to OH 3.4.5, so you’ll either need to work around this or see if the problem persists in the latest OH 5 milestone and file an issue if it does.
To work around it, I can think of several potential ideas:
- Open Reminder [3.3.0;3.4.9) or Threshold Alert [3.2.0;3.4.9)
- link all of the channels to one status Item and put the expire on that status Item
- crate a status Item that gets updated when the members of the Group update and set the expire on that Item
- implement a Design Pattern: Motion Sensor Timer
I’m pretty sure you cannot send UNDEF and NULL as a command, only an update.