Hi Murat,
My first thought was that your results are saved in SST2 format (deafult in your MMSIM version) and when your file gets over 2G size then the display would stop is using wavescan. Well, assuming 18.5ms would dump a big enough file to reach the 2G limit, I was going to propose switching back to psf and use the chunk option.
But since this behaviour occurs for even an inverter, then I would advise checking your data integrity. i have seen similar problems with people loosing data when running over a load sharing system.
Well, I still believe there is something wrong and you need to check your Unix files.
Going back to the first big file, give it a look at the following:
http://www.designers-guide.org/Forum/YaBB.pl?num=1238006736/1#1Would you mind posting your Cadence versiuon as well ? i.e. icfb -W
and tell us which viewer you are using: awd, wavescan ... etc