I have had the situation the OP talks about happen to me - not being able to book a 4th FP+ for any park (original or different)
It was back in June when 4 of us were touring together - 2 of them decided to skip their fastpasses and hang by the pool
DD and I went to MK and used our FP+ - we were unable to book a 4th no matter what we tried
I attributed it to the fact that the other 2 never entered the park with us and never cancelled their FP+ (just my theory since this was around the time Disney was instituting policies about catching fastpass overbooking)
It was back in June when 4 of us were touring together - 2 of them decided to skip their fastpasses and hang by the pool
DD and I went to MK and used our FP+ - we were unable to book a 4th no matter what we tried
I attributed it to the fact that the other 2 never entered the park with us and never cancelled their FP+ (just my theory since this was around the time Disney was instituting policies about catching fastpass overbooking)
