Why are my iCloud events not syncing with Outlook?

My wife and I use to syncronize the agendas in a shared Calendar on the iPhone, and this always worked smoothly. When I try to synchronize the same Calendar on the MS 365 Outlook work account, things get weird.

I've managed to add my iCloud account in Outlook (generating an app password) and I'm able to see the Calendar in Outlook, problem is: only full-day appointments are getting synchronized (I only need to download them, I'll never set anything on the shared Calendar from Outlook), while the smaller ones (like 1-2 hours events) are not showing at all.

Any hint? (thanks in advance)

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