Do you have any calendar entries with old dates? I don't know the cutoff, but I had a couple of repeat annually birthday entries from the 1920's and one for Texas Independence Day in 1836 that caused huge problems. Lots of unresponsiveness and repeated entries showing up on every day instead of the correct day of the year.
Once I moved my old entries to have a 2000 start date (and kept the repeat annually setting), everything is working well.