Hi David,
Thank you for posting this. While you can delete and reinstall mSecure 6, most times the reason why Face ID isn't being displayed as an option in the new app is because it doesn't have permission to do so from iOS. In order to fix that problem, you can either reinstall the app, which will fix the permission issue, or you can open the Settings app, tap mSecure on the main page, then turn on the "Face ID" toggle. That will add the permission needed, and you should then be able to use Face ID to unlock mSecure again.
David
for those having problems with Face ID, I found that if you have an older version of msecure and you download or upgrade to new premium MS5, you may not see an option to enable face ID. I finally solved this problem by deleting old and new app, and the reinstalling only new app. MAKES SURE YOU ARE BACKED UP FIRST!