did you check with the docs?
it is depending on the device difficult to get a constant ping - that’s why sometimes you have to work with proxy items and get them some more expire-time. It reduces the false negative - but of course heightens the risk of getting to know offline-items at a later time…
if you use the gMonitoring “item”-group, you can of course check the group - no need to check it with things (which from the OH-concept don’t make sense to put in a group)
on a side note: OH3 bringt a whole new way of seeing things, items and stuff with the concept of a “model” openHAB 3.0 my getting started notes: Model and Pages