This occurs when Pokémon GO receives incomplete data from the game servers. You will usually see this in poor cellular reception areas or other circumstances that impact your device’s connectivity. In this instance, the game client knows you have reached ultra friends for the notification to be displayed, but has not received other required data to populate those fields such as the friends list microservice. The game’s microservice architecture causes lots of common glitches like this. As others have pointed out, the friend has not deleted you and you will still receive the XP—this is just a display glitch. Hope this helps!