My guess:
The call, "Go around, Flaps 20" made by a crewmember
"Set thrust" or "Check thrust" call is not made because it is not required when autothrottle engaged
Autothrottle disconnect switches are pushed rather than the TO/GA switches
No one notices thrust is still at idle
No one notices nor calls the FMA modes, which are not "THRUST" "TO/GA" "TO/GA"
Someone calls "gear up" without having verified a positive rate of climb and/or
Someone raises the gear without having verified a positive rate of climb
Pitch is increased, airspeed decreases and plane settles onto the runway
Just my guess...