Judging from my previous comments, you are not loading the XML file from the same Fiji instance from which the XML file was written? Maybe, you also have updated TrackMate in between? You can check for the TrackMate version that has created the XML file by opening it in a text editor of your choice and looking at the second line in the file:
<?xml version="1.0" encoding="UTF-8"?>
While you have the file open, you can also check if you have spots in the
frames > 5 by searching for the following tags:
In general, it is always a good idea to go back to the version that was used to save the XML files.