Where did my read emails go?

I have an XR. One minute all my emails are there...the next they have disappeared. The mail icon on my home screen had the number of new emails I had received, but when I went into my emails, none were there. Not the old ones that I hadn’t deleted and not the new ones. Nothing to do with the ‘unread’ filter. All other folders have the emails, it’s just the inbox.

Since then I have checked my emails from outlook website (it’s a hotmail address) and all the emails that had and hadn’t been read are definitely there, but just not in my mail app. Is it a syncing prob?

I rebooted the phone... twice since then and I can now receive the new emails, but still can’t see the ones I have purposely left in my inbox. So frustrating!!!!

Anyone got any ideas?? It’s definitely not about the read/unread filter at the bottom left of screen.