Unity Ad failing to load after being played several times

Unity ads were working normal, I didn’t update the game, but after watching the ad several times successfully, I couldn’t play more ads. My guess is that I watched the ad too many times and was disabled from watching them, could anyone confirm my guess,or find a different explanation?

Hi, I have the same problem. Have you figured it out?
(I described my problem in this topic AdMob rewarded Ad fails to load after several success ad shows - Questions & Answers - Unity Discussions)