So I just checked Freisen's match in question. In their starting seven they have a German setter, German OH and German libero. In the first set against BBSC Berlin, they replaced the German OH with a foreign player for the last few points of the set. Apparently the rules posted above don't apply for starting six plus libero but for actual "players on court" which is probably what broke their neck. If the libero hadn't left the court while the foreign OH was on, nothing would have happened, but now it seems they'll lose the match because of that
I have checked this. With the score at 20:24, the Freisen libera leaves the field and only one German player is left.