The campaign quest Training Wings is unable to be accepted until Whelptender’s Wisdom is completed due to the quest giver, Amella, being phased. There is no indication in the UI that this is what’s happening, the map screen just says to continue the campaign by accepting Training Wings from Amella in Ruby Lifeshrine. Amella can be found, but offers no quest until Whelptender’s Wisdom is completed.
Note: This has an easy workaround, just complete Whelptender’s Wisdom, should take about a minute.