If the password for the POP3 account has changed since it was setup in webmail did you remember to update it there also? No, then do so under ☰ > Settings > Accounts
If Outlook is configured to receive emails using:
POP3 then seeing them there would suggest that it was first to download new emails and webmail then has nothing (new) to download
IMAP then webmail should have received new emails to its Inbox provided they had not been moved to another folder in Outlook
NB: webmail's POP3 account folders are stored locally so unless an action was performed to populate the folder it would not have any content, for example a send action would populated the local Sent folder and receive action the Inbox folder.