All calendar entries were deleted after the upgrade. No entries are read during sync either.
maybe https://lists.archlinux.org/archives/list/arch-general@lists.archlinux.org/thread/F4IPTWJZVYWAU5YTVKVIOG5NGJMONV5K/ ?
not much to go on and no response for a long time. I'll close then. feel free to re-open if this still happens and if you have more info