(1) The only time that Sleep resumes instantaneously and correctly is by manually pressing the power button, followed by a second press within about 5 minutes.
(2) If the interval is longer than 5 minutes, the Sleep converts to Hibernate. Resume launches the Dell logo, and takes several minutes. Some apps may not be correctly restored. The main victims are Edge, Thunderbird, and WhatsApp. (Of course, as soon as Edge is clicked, it offers to restore all tabs.)
(3) If Sleep occurs naturally when I'm away from the laptop, then the Sleep eventually converts to Hibernate, with the Dell logo on resumption, and Edge, Thunderbird, and WhatsApp not restoring.
(4) If I initiate Hibernate myself, resume behaves as above. It never resumes correctly (missing apps).