I have no idea; besides my sleep turns fix last week no one has touched Gen 1 in several months. It's probably just the server dropping EVs again, which would be easy to check if challenge matches were logged, or a console admin were around at the time.
Edit: After looking at the replay more closely, the Tauros in question did in fact have no EVs, since it had 290 max HP.
teal6 and Typhlito, that's a really weird problem where apparently only Ty's Tauros's DVs weren't registering. A redo would be best, yeah. Marty's looking more into the issue, so hopefully it's figured out before you guys battle again. Just in case it's the importer, you all might want to use the teambuilder for now.