@DCContrarian: thanks, that indeed solved my problem!
@Ran Talbott: I'm running on an Arduino UNO, using atmel328 if I'm not mistaking. I thought all the execution paths had a client stop, strange I'll investigate that further (I want clean code).
Not sure if it was at a 'certain' number, my impression was that it was rather variable amount of connections, but i didn't check that. The server is definitely working ok, that was verified.
Thanks for your replies!