Notes rarely sync on their own between iPhone and mac - why?

For years I have used notes both on my macs and my iphone. Until recently if I modified a note on any one device, it would update across all the remaining devices within a few seconds.

A short while back I noticed that notes no longer do this. If I update a note on my mac - it will not sync on my iphone unless I shut and then reopen the notes app on my iphone - and even then - if often takes a reasonable time to recognise that the state has changed - and to perform a sync.

I am not entirely sure whether the issue is as bad the other way round. So - if I update a note on my iphone - I cannot definitely say that the notes on the mac do not always sync. I do know that reasonably often they are not synced when I first go to notes on the mac - but the mac notes then recognise the state change and update.

It is almost as if some or other state broadcast has been turned off between devices in the near past.

I have ensured that I am signed in on all devices with the same user name, iCloud is activated (for notes too) and the myriad of other suggestions on the net. The very fact that after reopening the notes on my iPhone they will then sync tells me that there are no account or other similar issues. To me it looks much more like a "state broadcast" not working...

It would be great to resolve this.

Graham