Hi A., and all,
It seems that `%page%` is only for sequence diagrams, then your diagram is not a sequence diagram (it is a use-case diag.,...):
to turn to a sequence diagram, just insert `actor` keyword, as:
@startuml
footer Page %page%
Alice -> Bob
actor Alice2 as a2
@enduml
And see the expected result with `%page%`:
Enjoy,
Regards.