Currently I have noticed that the mopub banner sometime does not show up the ad but leaves a message “Ad Unit (XXXXX) is still warming up. Please try again in a few minutes.” although that ad unit has been worked for a long time before. This issue makes my fillrate go down alot*
I’m getting this today as well. I turned off the Marketplace and now just have Millennial Ads and that seems to work much better.
I know that Mopub were doing some ‘maintenance’ which wasn’t supposed to affect ad serving.
Thanks, I will try to turn it off 