Please try increasing timeout for ECP to resolve your issue above.
PLease Launch Command Prompt using Elevated Mode and ran the following commands:
Appcmd add backup "BackupTimeOut"
Appcmd set config "Default Web Site/ecp" -section:httpRuntime -executionTimeout:2400
Appcmd set config "Exchange Back End/ecp" -section:httpRuntime -executionTimeout:2400
Like the discussion in this similar thread: Exchange 2013 Request timeout when trying to edit Distribution group
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If that does not work your server is most likely overloaded and needs to have more resources allocated to the VM.
Check for Mailbox Database corruption errors in the event logs on the Exchange server
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