incoming emails randomly deleted (ie never delivered), not in trash or junk folder

Hello,

I have recently noticed that a number of incoming emails are being deleted, apparently at random. 

They do not go into the junk email or deleted folder, they just never arrive.  This has happened to at least five emails (that I am aware of) over the past few days.

I was using my iPad mini email app at the time and when this happened, I had a new email notification but no new emails.  The notification disappeared after a while. 

After realising what was happening and talking to a few people I was expecting emails from it transpired that, on the Monday alone, four emails were not delivered to my inbox.

I've stopped using my iPad email app for the time being but I'm not sure if this is a Hotmail problem. 

I remember in the past that, on several occasions, my number of unread emails when using my laptop indicated a new email (there was none) and after a few minutes it changed back.

Does anyone know why this is happening and what I can do to fix it? 

Thanks,

Jennmw