In short, it's a bug introduced in the 3.17.7 release of aView on August 13, 2019 and you shouldn't see the yellow/on-notice status.
From what I can tell, it supposed to mean the device is unreachable, but it has checked into aView at some point in the past (i.e. it's not down, but it's not up)
On the Dashboard of aView, the "Connectivity" pie chart in the middle of the page lists a count of devices that are up/down/unreachable. The "on notice" bug only applies to devices that are in the "unreachable" status in aView. So you could click on the Unreachable slice of the pie chart and aView will redirect you to an index page that lists just those devices. From there, you can sort the table by Status/WAN, which will group all the "on notice" devices together.
The "on notice" status shouldn't prevent the device from receiving firmware updates. It's strictly an issue with the aView site marking the device with the wrong status. The device should be listed as up/green instead of "on notice". The aView team is aware of the issue and are looking to release a patch to aView soon to resolve the issue.