Yes you can delete that whole line, or if you have the correct data to put in that line that should work as well but that can be pretty tedious.
Another option is to copy over in your data folder the latest good data backup that Cumulus creates, with Cumulus stopped. Then when you restart Cumulus it will download from your data logger from the date/time from that backup (presuming your data logger has the data since that latest backup. If your log files have a shorter interval than your data logger this may not be your preferred method.
Removing the whole line is the easiest, and you would not lose much data.
Likely some glitch in writing to the file.
Paul