Found in aoe age4 12.0.1974.0
In the hotkeys list, the verb “focus” is used to indicate an action of selecting and snapping the camera to its object(chosen inconsistently), except in the “Focus selected unit(s)” hotkey.
What it does is similar, however not the same as it makes the camera follow the “focused” units.
This behavior is identical to the “Follow selected unit” hotkey thus redundant, and does not follow the consistent usage of the verb “focus” in other hotkeys.
Expected behavior should snap the camera to the units like double-tapping control group hotkeys and nothing else.
This bug is reproducible by pressing F5 with the “Default” hotkey profile.