For B1516_0607_heIL_dsk_p2_sm_pym_adyen in the 6/7 test, BannerLoader sent back some js with "bannerHtml" set to

"\u003CCentralnotice-template-B1516_0607_heIL_dsk_p2_sm_pym_adyen\u003E"

which is what you get from msg() when the key doesn't exist.

Making a dummy edit to the banner and re-saving cleared up the problem, but there's still way less traffic than expected.

Throw an exception to log the problem and tell the front end that no banner was loaded so impression logs are correct.