Reproduction - have your hero exploring a wildlands, so that there is not an adjacent square that is not wildlands beside them.

Then trigger enough fame to get another hero (eg finish a quest with another hero taking you over the breakpoint).

You get to choose a new hero, and they appear in your list of armies, but if you click on them, the map does not zoom to them, and you cannot find them on the map.

I've had this happen twice now, and this second time, I've managed to rescue the autosave and keep it, and it is reproducible, and moving my sovereign out of the wildlands prior to finishing my quest results in getting the new hero normally.

Will email the save to stardock support and link this thread.