I see, that means that those log files are no longer indexed. Either you have index retention of 29-30 days or your emergency maintenance got triggered.
You can verify with "ls -lh $RTDIR/log_indexes/". Anyway I recommend looking at your log retention definitions on the log server object.
I will suggest one of the following actions:
1) If you only want to retain the log file you can always copy it back to the server and open it. Log files are located in "$FWDIR/log/". Make sure to copy all files with the same date - log file has a few smaller files with relevant data which are important as well.
2) Use SmartConsole as you suggested - a) open log file b) Filter the logs as much as you can c) Scroll down until you have all the results you wish and then export
3) Try to open CPlgv.exe from the SmartConsole directory. This is the old tracker. You can open the log file you desire and export it to txt (menu -> file -> export). This might not work depending on your version.
Kind regards, Amir Senn