Problem with syncing Calendar attachments between MacBook and iPhone via iCloud

I have a very strange problem with syncing Calendar (via iCloud) between MacBook and iPhone. Namely, the events themselves are synced, but the attachments to them are not.

I create an event in the Calendar app on my Mac, attach an attachment to it -- the event appears in the Calendar app on the iCloud website and on my iPhone, but without the attachment. And vice versa: I create an event in the Calendar app on my iPhone, attach an attachment to it -- the event appears in the Calendar app on the iCloud website and on my Mac, but without the attachment.

What's interesting is that if I create an event on the iCloud website, and then add an attachment to it on the Calendar app on my Mac or iPhone -- this attachment syncs perfectly between all devices.

How can I solve this problem?

Hardware: MacBook Pro M1 Max (MacOS Sequoia 15.0.1), iPhone 14 Pro Max (iOS 18.1)