The calendar list does not support dates when computer has a danish (european?) setup.
The first screen shot shows how the dates are represented in Google sheet.
It is how glide has specified it (MM/DD/YYYY)
But when you look at it in the glide builder (in app on iOS it is ok) it shows up as june and december entries.
Try also to look at how Google sheets interprets the date - the are interpretted all as june
So to me - this is a bug.