Unity Ads Interstitials are showing but Banners are not

We implemented Unity Ads on our Android game, and the test samples (“this would be your banner”) displayed properly in test mode.

However, after getting rid of test mode and making a build, banners are not showing, while interstitials are working just fine. I’m getting the following errors:

Banner_Android Placement Banner_Android failed to fill!
No fill for placement Banner_Android

I’m also getting this error every time I try to reload the banner (after calling Advertisement.Banner.Hide(true)):
A Banner is already in use, please call destroy before loading another banner!