Thank you for your help - mine were all ticked so to no avail.
Oddly, although the emails have gone missing in the webmail and my ios devices, on the ios devices, if I can not see them but type in subject or key word they come back so I can open them.
For example, earlier I typed in "blinds" to find an email for an order I placed last year and the email which had been left in the inbox appeared and I could open it etc. When I closed it it was gone again (but I could get it back via search). If I try that on webmail it makes no difference.