Calendar fails to sync

I've been away for the weekend, although within WiFI "earshot" at almost all times. So, when I added an appointment to my iPhone, I expected it to appear on mac mini and iPad. It did on iPad, which was with me and on same WiFi network. But, several hours after getting home, it still hasn't appeared on mac mini and has now disappeared from iPad!

I recently had the opposite, where something on mac mini didn't sync for hours onto my mobile devices (which I was going to use to get the postcode to use SatNav. Ended up writing postcode on paper!

For me, Calendar synchronisation is an absolutely key application on which I am highly reliant.

This is likely to be the last straw for this particular camel. I dare say other cloud diaries (say Google) have some problems, but in this particular respect, calendar now has glitches I've never experienced before/in previous versions.

Anyone have any ideas?

Thanks in anticipation,

Ian