Both items grant "advantage on Wisdom (Perception) checks". Is it because the Rod of Alertness is not technically equipped like the shield is?

I can confirm that the sentinel shield adds +5 to passive perception when equipped but the rod of alertness does not when marked as in use and attuned.

The Rod has been fixed now, thanks.

They now give +5 each, resulting in +10 if you have both equipped. You should only get advantage once?

Yes, you should get it only once since it comes from the advantage on Perception. But with the current modifiers, it is not possible to do that.

I will ask an official stance for this.

Eyes of the Eagle is not adding to passive perception either.

Quote from Revenant >>

[Tooltip Not Found] is not adding to passive perception either.

 Thank you for the prompt response, filcat. Luckily my character doesn't have both items, but I feel like a can of coding worms has been opened.