The only time that my Elite status was not recognized was when I was flying TK 2 days after I become Elite. I had booked the ticket when I was Classic Plus and on the travel date I was Elite as both the TK website and the mobile app. However, my BP still indicated Classic Plus. However, it was a domestic flight that I flew alone so I had the same privileges except guesting some one at the lounge which didn't matter to me at that time.

For United I never had issues, even for reservations on hold my Elite status was always visible.