On the homepage of http://www.shopifyexperte.de/ there are two flex-box modules, one under \"Kundenstimmen\" and one under \"Neueste Beiträge...\". The inner boxes are suppo
This is indeed a Safari bug. The details are available at the excellent flexbugs page, but to quote it:
Safari uses min/max width/height declarations for actually rendering the size of flex items, but it ignores those values when calculating how many items should be on a single line of a multi-line flex container. Instead, it simply uses the item's flex-basis value, or its width if the flex basis is set to auto.
So the fix / workaround - as suggested by other answers here - is to set the flex-basis to an explicit width rather than auto.