Perhaps it's because Rhea Gladiator aura trigger after the previous attack that trigger it resolved, while Rhea dragoon's refresh triggers during the attack itself. It doesn't bother us that much in pve, but with how arena turn works, this may be what caused your problem. Especially if what triggered the aura is the very last attack of that round.
If gladiator's aura activates in the midst of attack trigger, I believe she'll still have her refreshed turn intact.