Delay in Displaying Third-Party Calendars in Outlook

Question

Hi Team,

I'm experiencing an issue where adding a third-party calendar in Outlook results in a delay of up to five minutes before it is displayed. Additionally, I have multiple synchronized calendars and frequently encounter problems where some calendars fail to open.

When I try to add a user’s calendar via Start → "3 dots" → Add → Search for a user from the address book, it sometimes takes up to five minutes for the calendar to appear.

The issue occurs in both the Outlook app and Outlook Web Access. However, in the new Outlook, the calendars load instantly without any errors—it works perfectly.

So far, we have tried:

Reinstalling the Microsoft Office application package

Creating a new Outlook profile

Unchecking "Turn on shared calendars"

Unchecking "Download shared folders"

Despite these steps, the problem persists in the classic Outlook. I've attached a screenshot of the error. Any insights or solutions would be greatly appreciated.

Thanks!