Over about a month of usage, I am getting the following problem with appointments using Sharepoint Sync

Calendars don't seem to have sporadic problems synchronizing properly
 - at times duplicate appointments appear
 - after being moved they sometimes change back to their original date and time
 - Sometimes they are changed to be an all day event
 - the categories are sometimes changed
 - the status is sometimes changed from free back to the default value of busy
I renamed a category - and got Task 'SharePoint' reported error (0x80004005). ...Try again ...HTTP 500.
 
In "Outlook 2013 > Account Setting > SharePoint Lists" I tried unchecked the "Update Limit" box.
This seemed to be an improvement with instant sync as soon as any change was made and seemed to be more reliable,
but then smarter mail started locking me out of the account with "Too many failed login attempts" - locking me out for 10 minutes each time.
I re-checked the "Update Limit" check box and that fixed the login problems but reverted back to the appointments problems.

I am using Smarter Mail build 6948 and Outlook 2013 on Windows 10.