FAQ - Frequently Asked Questions & Answers thereof

There are Android apps which do not close calendar access correctly. This can lead to a blocking calendar. Currently apps like "NoLed" or "Smooth Calendar" are known for such a behaviour. Try to stop such apps and services and try the sync this way.

According to the information from the makers of "NoLED" there is an update now. It should be sufficient to deselect Calendar from "Toggle Notifications". Then select "Calendar" under "Monitored Apps" and put a check mark next to "All other". When prompted to give NoLED Accessibility rights, they need to do so as well.