Hi ASTRO24
Thanks for the input
I have 5 devices, 1 main ipad plus iphone plus an iMac and other older ipads all turned on intermittently.
The ipads / iphone are all updated to latest iOS so safari also up to date
The 'old' iMac still on Big Sur where it must remain unfortunately but also up to date
I emphasise that this a random issue, some icloud incomings are not affected, when they are I'm pretty sure it only happens after I've opened one of the other devices as well as the main one
No idea why that should happen, certainly no deletion on my part.
So I've now closed down the Mail app on all devices apart from the main ipad, no great hardship.
i will be switching to a new isp at the end of the month and watch with interest whether the problem is still there.