The script looks ok.
From your previous script run output I deduce that the TagCategories are all already there.
But the Tags in those TagCategories apparently not.
Can you check with
Get-TagCategory
Get-Tag
And can you
- do a trial run with a smaller CSV file. Perhaps 4 or 5 rows. This to better see what is happening.
- remove the pipe to Out-Null on the New-TagAssignment line. This might be hiding some messages from the cmdlet.
New-TagAssignment-Entity $($_.Name) -Tag$tTag