I couldn’t reproduce the problem with Android 8.1 (emulator) and an iCalendar which I have created from your event data. However, I noticed that it seems to contain
RRULE:FREQ=DAILY;BYDAY=MO,TU,WE,TH,FR – maybe this unlimited number of instances causes problems on your device, for instance because there’s no more memory to store the instance data? This could cause the Android calendar storage (which does
RRULE expansion) to crash, which would then cause an empty response to DAVdroid.
Does it work when you use no or another
RRULE with a limited number of instances? How much (disk) memory do you have on your device? What happens if you delete this event – does the problem occur for other events, too? Do you have another Android device where you could try synchronization? Is there any other way to reproduce the problem, so that I can get an idea?