Jun 11, 2020 04:33 AM|asplearning|LINK
I finally found the reason. It's because of one property call nextDayThreshold. Here is the explanation.
For some reason fullcalendar v.3 the threshold is set to 09:00:00 instead of 00:00:00. So we have to manually add
make it appear correctly.
Hope it would help others too.