iTunes add to Play next, query

This "facility" seems a bit flakey to me, of course it could be self induced. By flakey I'm mean sometimes it works and sometimes it doesn't

Using my Mac Mini, I have tried to add to the playing album list. Options are Play Next and Add to Up Next, I'm sure it used to be if selecting the second option new album was added to end of the tracks of the Now Playing Album, seems now that it inserts new album tracks after the current playing track.

iTunes v12.2.1.16.