How did you add these shared mailboxes, automapping with full access permission?
Did it work fine before? Sorry, your screenshot is not uploaded successfully, could you upload it again?
Based on my experience, this issue may be caused by Outlook client, you could test in OWA and check if this issue persist.
In addition, does this issue occur on other users? This can help us isolate whether this issue is about your mailbox.
As we know, when you have many shared folders or mailboxes open, you may experience slow performance event get errors. So could you please test to reduce the number of shared folders or mailboxes that you have open in Outlook. For Office 365 mailboxes, we could use SARA tool to troubleshoot the Outlook client issues.
Support and Recovery Assistant is a new tool that helps users troubleshoot and fix issues with various Office 365 apps and services. The app diagnoses common Outlook issues like account setup, connectivity issues, password issues, or Outlook stops responding or crashes.
https://support.office.com/en-us/article/about-the-microsoft-support-and-recovery-assistant-e90bb691-c2a7-4697-a94f-88836856c72f?ui=en-US&rs=en-US&ad=US#/?env=ExRCA
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