I recently had to repair an ADIF log file and came across a free utility called ADIF Master.
The utility allows you to import an entire WSJTX log file and "split" the file to create a separate ADIF file for a specific period of time (such as the MSQP). It also allows you to review and edit your file before submission.
Certainly easier than editing one giant log file with a text editor...
73,
Mark Braunstein WA4KFZ