The import of data from a text file has 2 modes:
1: the number and sequence of files matches exactly the number and sequence of records in the text file. One record is represented by one line of text, terminated by the paragraph termination characters carriage return and line feed.
2: a record contains one piece of data that represents the filename. Then the data of that record is assigned to the tags in the file according to the rest of the mask.
The number and sequence does not necessarily have to match each other.
So you have to decide which of the 2 modes you want to use.
If you can, use mode 2 as this leads to the fewest surprises. You would have to find a way to get the field for the filename (with extension), though.
For the import in mode 2, select all files, even if they do not have a matching record or even if there are more records in the text file than there are files. This should work... as long as matches are found.