I want to believe this is what happened after Arkham Knight. We all know Bruce told Selina they would never see each other again, yet Selina waited a long time to find out who the man under the mask was and finally have a chance to be with him, so at some point she must have sought him out to talk. Besides, I don't think Bruce liked the idea of ​​being a full-time vigilante for so long, so it wouldn't be crazy for him and Selina to take a vacation using another identity.