As part of our 4.0 release, we introduced some rendering changes for the components to unify their rendering. I am sending a modified version of the REPL link where the changes are taken into account and the Upload works as expected. Can you confirm that?
It is 4.01. I updated the REPL in this answer from 4.0.0 to 4.0.1, and it went from working to not working.
https://blazorrepl.telerik.com/wduQPzGl08ReuqHl49