Steps to reproduce:
Create series(recurrence) event in egroupware calendar with videoconference option on (no end date set)
When event time is reached, i can click to videoconference link in context menu on the first event
After a few minutes (~30min) the link from context menu disappear from all event in the series (and the videoconference checkbox is empty)
The test event that i created: alll weekdays at 10:00 eg.