Well let us know the route, date and departure time if you want help.

It can mean that it is full, especially possible for Eurostar or Thalys.

Let us know

This seems to be happening to more travellers lately. Please make an error report to Customer Support using the link below. 

https://eurail.zendesk.com/hc/en-001

If this is about a train that has disappeared from a trip in the app, then that doesn't say anything about seat availability. The app does not know anything about that.

Indeed report this to customer support and check this article:

https://eurail.zendesk.com/hc/en-001/articles/4571649483165-Contacting-us-about-an-issue-

Here is the train for those of you asking. I will report it today. Thanks! Let me know if this changes anything 

OK, so it disappeared from the app? Then it usually helps to restart the app or your phone.

You can also change in Visp. You'll have a bit more time there (11 minutes instead of 7).

You can book the EC Visp/Brig-Milan on tickets.oebb.at: add the Interrail/Eurail discount and the select "One-way tickets and day tickets”. There are still seats available, price is €11 in 2nd class and €13 in 1st.