Common fixes
What fixes the Z5 II's known problems — soft frames, a missing detection box, video that stops, a second card that never fills?
Shutter shock, and d6
Portraits soft at 1/60–1/200 with focus confirmed: the mechanical shutter's own curtain movement is blurring the frame. Custom Setting d6 [Shutter type] set to Auto uses the electronic front-curtain shutter at slower shutter speeds (where shock lives) and the mechanical shutter at faster ones. EFCS's fastest shutter speed is 1/2000, which is why Auto never asks it for more.
The detection box that never appears
Subject detection runs only in Wide-area AF (S), Wide-area AF (L), Wide-area AF (C1), Wide-area AF (C2), 3D-tracking and Auto-area AF. With Single-point, Pinpoint or Dynamic-area AF selected, the camera focuses where you point and detects nothing — silently. The fix is an area-mode change, not a setting inside detection. With manual-focus lenses, MF subject detection area (All or Wide) performs the same rescue.
Video that stops on its own
Three clocks: the 125-minute per-shot cap; the heat countdown that appears after high-temperature warnings (Auto temperature cutout → High delays it, at the cost of a hot body); and the battery — an EN-EL15c delivers about 85 minutes of video, usually the first limit reached. N-RAW takes also depend on card rating: V90 is Nikon's recommendation.
The second card that never fills
The factory role for Slot 2 is Overflow — a spillway. Set Backup and every picture is written to both cards. Videos ignore the stills role entirely: their card is Video Recording Menu → Destination, which must be set separately or clips stay on a single card.
Set d6 to Auto, move to a Wide-area mode, set Slot 2 to Backup, point Video Destination at the card you mean, and check your temperature policy — then shoot a slow-shutter portrait and a two-minute test clip to watch all four fixes hold.