My Photo Stream is not necessarily identical on all your devices. My Photo Stream is only buffering the new photos in iCloud, only the photos you imported to your library during the last thirty days, and at most 1000 items. If you turn on My Photo Stream, after it has been disabled, you will only see the new photos, that are currently in iCloud. Your other devices may still have older photos cached from My Photo Stream, that are no longer in iCloud, up to thousand photos. But turning off My Photos Stream and then turning it on again on a device is resetting it to what is currently in iCloud.
If you import a new photo on your Mac Book Air, does it appear in My Photo Stream on your iPad and iPhone?
Is My Photo Stream empty on your MacBook Air or is it not shown at all?
If you are not seeing it at all, you may have enabled iCloud Photos im "Photos > Preferences > iCloud". If iCloud Photos is enabled, the My Photo Stream album will be hidden.
Get help with My Photo Stream - Apple Support