Recaptcha Enterprise scores dropped significantly since about a week

When checking the score-distribution on https://console.cloud.google.com/security/recaptcha/

the scores dropped from this (first week of June) 

to this (first week of July)

Obviously, this has a major impact on our users (schools & pupils, often starting our app at more or less the same time)

Any idea why this is happening?  What I can do to improve this? ...