eM Client IMAP will not download/display security code emails from Facebook.
The emails are there on the server, but eM Client pretends they aren’t there.
Tried repairing the inbox
Deleted and rebuilt the account
Other email clients display these emails with no problem. Why would eM Client decide that these emails are invisible?
Have you looked in the Spam / Junkmail folder ?
If it is in your Spam / Junkmail folder could be you might have eg: accidentally blacklisted that FB email address or FB Domain with the security code so it goes straight to junk.
If you have up to V9, you go to “Menu / Rules” and “dblclick the blacklist” to view address’s
If you have V10 you go to “Menu / Settings (Preferences) / Mail / Blacklists and Whitelist”.
Then click “Manage Blacklist” at the bottom to check as per the eM Client documentation and screenshot example below.
Or could be the missing FB Security code email is in eg: another Inbox Category tab if you have V10 and have Categories enabled, so then email doesn’t allways show in your primary Inbox tab.
See below Blog page on Inbox Categories
nothing in spam/junk
nothing under blacklist
have moved on to another email client 
thanks anyway
