Long Time To Write Metadata

[Darius1968]

The attached log file (in debug mode) is being submitted for analysis, after a metadata write-back for 18 MP4 video files took about 5 min.  Thanks you. 

[Mario]

99% of the write-back time is spent by ExifTool.
MP4 files are usually huge, and adding data to them, splicing when needed etc. takes longer. Linke everything with video files.

I suggest you reduce the number of threads used for parallel write-back if your system slows down that much when multiple video files are written at the same time (Edit > Preferences > Application).
Store the videos on your SSD unless they are fully processed, then move to long-term archival storage.