Why do semitailless swept-winged aircraft, but not delta-winged aircraft, suffer from (primarily) pitch oscillations at high mach?
The function of a &quot;tail&quot; in this case is pitch stability.  Therefore, all stable aircraft must have &quot;tails&quot;.  Aerodynamically, the rear portion of the delta is its tail.  Removing it should have predictable consequences, even in the subsonic realm.
Transonically, with shock waves dancing on the wings and a moving center of pressure, pitch stability is critical.  This is also true in slow flight, where a shifting center of pressure can overwhelm weaker pitch stability.
Subsonically, the swept tailless design can be helped by &quot;washing out&quot; (lowering the AOA of) the wing tips or by adding slats, which helps control movement of the center of pressure at higher angles of attack.  As Dunne ingeniously realized over a century ago, this design made for a stable aircraft.  Indeed, a swept wing aircraft with insufficient tail area could be helped with stronger slats!  (If the wing tips can handle the extra load).
Transonic and supersonic flight is another issue.  The notion of &quot;taillessness&quot; was a blind alley in aviation design, a mistake not to be repeated.