Hi, welcome to the forum!
If you have shuffle turned off, "Queue Random" is "Queue Last", playing the selected tracks after all other tracks. With shuffle on, "Queue Last" is meaningless because the tracks at the end of the list could be played at any time. Instead, tracks are added randomly among your ENTIRE Playing Tracks list. If you have hundreds of tracks in the list, it's entirely possible to have 50 go by without the queued tracks being played.
If you want the selected tracks to be played immediately, you should use "Queue Next"