Created an event that repeats every two days, starting on the 7th of month with the first instance ► occurs on dates 7, 9, 11, 13, 15.
Dragged the second event in the series to the day before ► occurs on 7, 8, 10, 13, 15 ◄ the 10th for the third event is a very unexpected result here!
Dragged the second item back to its original date ► 7, 9, 10, 13, 15 ◄ third event stays in odd spot...

I also dragged a yearly recurring event back one day and it disappeared from the calendar view. I have since made some changes that prevent me from checking where exactly it went but there was definitely something fishy at play there.

As always, many thanks for looking into it, Pierre.