I have tried different versions of oscam, and tried to adjust settings, but still the same.
But now I have got a clue of why some channels have problem with lagg/freze.
from time to time I get message in the log file that indicate that timecode of the transponder is wrong, and found somewhere on the web that the message indicates that oscam believed the key received from the card was expired.
Temporarly I have solved this with using an CanalDigita receiver when watching the channels with lagg/freeze.
I have also discrovered that all channels with problem is on two dvb-s transponders. all channels on other transponders (dvb-s & dvb-s2) is ok.