so the airplane doesn't have a target altitude to level off
we have set missed app altitude in FCU. and by FCOM
The ALT mode maintains a target altitude. This target altitude is either the FCU selected altitude or
an altitude constraint delivered by Flight Management.
ARMING CONDITIONS
Applicable to: ALL
The ALT mode arms automatically whenever the aircraft climbs or descends toward the target
altitude.
Note: The ALT mode arms only if the difference between the current altitude and the FCU
selected altitude is at least 250 ft.
When ALT is armed, the FMA displays the ALT message on its second line:
‐ Blue when the target altitude is the FCU selected altitude
‐ Magenta if the target altitude is an altitude constraint.
as per the note its applicable for takeoff phase, in fcom nothing is mentioned about goaround phase.