There is a known issue with the file editor not being able to access the lab’s filesystem. When this happens, Open and Save buttons will display empty dialogs, like this:
If one of your students encounters this, please have them follow these instructions:
Close the browser tab of Strigo.
Wait for about 30 seconds.
Navigate to the training event's URL again.
Try to use the Editor again.
This is a known problem on our side, that has to do with a user trying to join an existing connection to the lab. By closing the tab and waiting a bit, the connection should be disposed and a new connection will be created when the student returns, and then the Editor and its filesystem should work fine.