I have recently run into an issue of my Outlook being unresponsive for several minutes at a time. I have about 9300 items on my calendar in Outlook. Every time someone responds to a calendar invitation (either accepts or denies it) Outlook becomes unresponsive for between 1-3 minutes.

Any ideas on what could be causing this? I have tried creating a new user profile, it still has this issue. The unresponsiveness is restricted to inbound calendar responses, not regular emails. I have tried moving items from one calendar to another; however, this process is lagging (takes about 20 minutes to move 10 items). I have turned off all rules.