Hithere, I have been experiencing similar issues on my M coupe, sometimes like you i turn the key and nothing happens or sometimes it is perfectly normal. Sometimes i hear a click and sometimes nothing. Is yours a daily driver or is it like mine and sits for 3 or 4 weeks unstarted and undriven ? I did 900 miles only last year and things seem to play up when not driven.
Still dont know if it is the starter as havent removed or tested as some on here suggested ignition switch as a pos cause. I have found an oe starter for £165.00 so will probably change to eliminate that. People have suggested to get a s/h ignition switch from a breaker but that goes against my nature as I would worry that that too could have issues due to being old and used. I havent priced a new one , it may be that they are not available or hiddeously expensive and that is why people go the used route. Any advice welcome. Good luck with yours and whoever fixes it first will hopefully post and help the other one sort theirs .