Missing modifications to recurrent events from last month

When displaying the events from the current month I get an error in the log like:

[https://my.xwiki.host/xwiki/bin/get/MoccaCalendar/Code/JSONService?xpage=plain&outputSyntax=plain&calendarDoc=MoccaCalendar.WebHome&filter=wiki&classname=MoccaCalendar.MoccaCalendarEventClass&startfield=startDate&endfield=endDate&durationfield=&outputView=month&start=2020-03-30&end=2020-05-11&_=1587980526858] INFO  m.s.MoccaCalendarScriptService - we dropped some modifications: [1]

Indeed I edited an event from last month, and this event is not shown in this month overview, despite of its actual date being in the same week as the 1st of this month and thus within the range of events to be displayed. I guess I moved it from the 29.03 to the 31.03, and only the latter is in the first week of this month.

The same modified event shows nicely if I page to the last month.