So I've sent a message to support and got an automated reply where this issue is discussed. After fiddling with both Google Calendar and Chronus, I now have the birthdays back.Somehow, the last version doesn't show birthdays in the calendar part of the Flex widget. The 'birthdays' calendar is selected and 'hide all day events' is off... (?) Help!
Weird part is that certain birthdays (for testing) now keep showing in Chronus, even though I removed them from my contacts and calendar!
A reversed problem :')