I took filename_csv.txt and renamed it filename.csv and opened it in a spreadsheet.
In the Shutter (speed) column, 1/60 was converted to a date, 1/1/1960 and same with 1/30, 1/15 but not 1/125 because it doesn't convert to a date easily. Maybe the shutter speed in the app should be stored as 1/60s, 1/30s, 1/15s, 1/125s and when it is a long exposure, 1s, 2s, 4s, etc. 1/60s stays as 1/60s in the spreadsheet (Linux Mint application called WPS Office).
This is not a problem with exiftool, it is your spreadsheet program. Open the CSV file with a text editor (such as notepad) and you'll see that the value is correct.
Your spreadsheet program is assuming that 1/60 is a date and displaying it as such.