I was on a flight last year in F with someone with the same initial and surname as me in J. When I checked in there was a duplicate booking comment but I confirmed that I was flying. The other person was a female and I wasn't which may have helped them realise that it wasn't an actual duplicate.

A few weeks ago when entering the lounge at NCE I was told that I had already entered. However, that could have been a simple mistake of the lady behind the counter putting a tick against the wrong name. Interesting how they always have the passenger list at the communal lounge in NCE.