Did you use the immersion chiller Leyther? My prime suspect would be the cold break, after chilling down rapidly that is the only time I have had a problem, one thing to try is getting a good whirlpool going and while everything is in the vortex open the tap.
No I've moved onto no chill, I can only get down to about 35c with the immersion chiller and a lot of water so still not pitchable anyway. Hopefully I've now found the best method.