The mouse cursor doesn't show with the windows screenshot, but if it did you'd see it 1 tile below my Sov's move-to X, and it'd be changed to the 'dialogue mouse cursor icon'.  You can see the card of the party's leader Joffrey in the pic.

Joffry's invisible party has 4 members.

I've seen other examples of this -- my hired champion (seen with me in the red robe) was also invisible when encountered (saw him because the cursor turned to the dialogue icon -- reloading made him visible).  This seems fairly common in beta 2A, didn't see it in beta 2.

Reloading does cause Joffry's party to show up.