If it’s your Gmail account could be that it’s just not synced correctly with your Gmail online. Or your Gmail account has become corrupted in some way, Or you may have an older version of eM Client and needs updating.
First thing try repairing your Gmail account in eM Client. Make a backup of eM Client first though via “Menu / Backup”.
To run the repair on your Gmail account in eM Client, “Right click” on “All Mail” folder (under your Gmail account" on the left side of EMC, and then click “Properties” at the bottom. Then click the “Repair” tab at the top. Finally click “Repair”. This will re-sync all your mail and folders from Gmail.
Note - Repairing can take time depending on the size of your Gmail mailbox.
Failing that remove your Gmail account from eM Client, and then re-add your Gmail account (via the automatic wizard) and make sure you click (Allow) near the end of the wizard to allow EMC access to your Gmail account.
Lastly if still same problem, check that you have the latest version of eM Client via the version history page and update if you have an older version. https://www.emclient.com/release-history