Spanish-speaking fandom always used it as a compound (fanficción)*, but mostly stuck with the shortened forms - fic -. The REAL issue is gender, actually. Most people in in my experience use a masculine form - el fic - but other people use the feminine form.

I've always seen it as one word, really.

* Separated, in Spanish, makes no sense and should be 'ficción fan'. Since 'fanficción' is a translated loan word, it had to be a compound in order to make sense.