Multi-Day Events Shorten to One Day

We have an M365 shared mailbox for our out-of-office calendar called ptocal@[domain.com]. The members of the shared mailbox go into the calendar and mark when people will be out of office. For one user (who happens to be the one who does it the most), when she puts in a multi-day event, a few seconds after saving it, the event shortens to only the first day. She is on Windows 10, using the old Outlook.

Has anyone experienced this before or have any ideas on how to rectify it?

I have already recreated her Outlook profile, removed and re-added the calendar, and made sure the computer and Outlook use the same timezone.