Huge number of duplicated Outlook calendar entries today

Further update – the items that have suddenly appeared in my Calendar today (from over 4 years back) seem to be Calendar items which originated from Invites from other people.
However the many many duplicated Calendar items going back years are NOT all derived from Invites – they are ordinary manually entered Calendar items.
Hope this helps.

Thanks for your prompt reply.
Hard to understand why or how Outlook itself would make duplicate entries – generally speaking any Outlook Calendar entry has to be physically created unless a recurring appointment I believe. I would say that it would need dedicated Outlook programming for the product to create new/duplicated items automatically?

Alternatively there could of course be some corruption with the Outlook database – but I ran the Microsoft check tool and no problem was detected.

Also I am seeing earlier calendar appointments (e.g. In June) that I know for certain I moved along to July suddenly reappear in their original date.

I know that any Sync tool is not meant to create duplicates but to do that there must be some aspect of the programming that checks to see that the entry on e.g. the iOS device is exactly the same as that on the originating Windows device and prevent it being taken copied from the iOS device to the Windows device. I would imagine that that is quite a tricky task to perform and that there is a small chance of ‘confusion’ and accidents happening?

All very odd – I’ll keep an eye out (as well as devote time to removing the thousands of duplicates) and let you know if there I spot any likely cause.