Why does accessing multiple shared calendars cause slowness/crashing?

Question

We have a user that manages the calendar for multiple individuals. When they click on meetings within their calendar, it can cause Outlook to hang for 10-30 seconds and sometimes cause it to crash completely. They recently had their machines replaced in the hopes that would fix it but it has not. Webmail works without issue. Outlook is 2016 32 bit. Users are all in o365.

Answer 1

I have a user with the same issue. She manages 8-10 calendars and when she opens Outlook 365, it takes a few minutes to display and then refresh the calendars. The calendars are not shared mailboxes....just shared calendars.

Answer 2

What's the version of your Outlook 2016(File>Office account>About Outlook)? Please ensure that you are working with the latest Outlook version.

We have a user that manages the calendar for multiple individuals.

How do you access and manage the calendars ? Via Delegate, calendar permission or other methods?

What's the specific number of shared calendars that you mentioned? To further confirm your issue, please try to add only 2 or 3 shared calendars in your accounts and check if the issue has any difference.

I tested a lot about your issue in my environment(Outlook 2016 MSO 16.0.4266.1001), using O365 email account to access 3 shared calendars by the calendar permission in Outlook. And found that it could work fine without any slowness/crash. So it seems to I were not be able to reproduce your issue.

In order to conduct further researches on your issue, please troubleshoot your issue by following the steps below:

1. If you are using an exchange account, please try to turn off your cached exchange mode(File>Account settings>Account Settings>choose your account>uncheck use cached exchange mode) , and check if the issue could be better in Outlook Online mode.
2. To avoid the interference of Outlook add-ins, it's suggested to restart your Outlook in safe mode(“Win“+”R “ > Type outlook.exe /safe > Click Enter) and see if the issue continues.
3. Corrupted profile may also causes this issue, please try to create a new profile(Control Panel>Mail>Show profiles>add) to test.

Besides, I found some other official documents which might be related to your issue. Just for your reference:
accessing multiple shared calendar or shared folders could affect Outlook performance,
Outlook performance is slow in the Office 365 environment.

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Answer 3

Take a look here: Outlook performance issues when you have many shared folders or mailboxes open
This applies to calendars as well.

https://support.microsoft.com/en-gb/help/3136059/outlook-performance-issues-when-you-have-many-shared-folders-or-mailbo