Recover missing Outlook email

Until a few hours ago my Outlook inbox had many emails, most of which were received before today. For some reason I can no longer see any email that had been in the inbox other than those received today. My email syncs across 3 devices, my PC, an iPad, and an iPhone. All 3 show the same results for my inbox, with the only difference as far as I can tell is that the iPad reflects all the emails as unread. I do not use filters or rules, nor did I delete those emails. Can you help me recover them?