Do you have Auto forwarding set up on the mailbox? Or mail filtering?
Do you collect messages on computer email client / phone app as well as webmail via a browser?
Unusual that messages only from 15 July are missing. Auto forwarding from that date is the best bet. Except if they were there until recently when it's most likely a new device connecting to the mailbox and downloading and deleting messages but only for the 30 days prior to setting up the new device 10 days ago.