Keynote 15.4 shows horizontal rendering glitch on displays

Keynote 15.4: Horizontal Rendering Glitch Appears on Both MBP and External Displays

Since updating to Keynote 15.4 (auto update yesterday, 9/30/26), I intermittently get a large horizontal rendering band when toggling into/out-of Edit Slide Layouts. The artifact issue appears whether I'm using my MacBook Pro display or a connected external monitor, so it does not appear to be specific to the display.

Artifact stays onscreen unless I do one of the following:

• Jiggle the Keynote window

• Move the Keynote window from one display to the other

• Make the Keynote window smaller then resize it again

• Go into Play mode, then out again

All of these force a redraw and make the band disappear. Restarting Keynote or the Mac does not prevent it from happening again.

A fresh presentation using one of Apple's dynamic themes does not reproduce the issue, but it does reproduce every time across a series of presentations I've been building in a 5:1 widescreen format which produced no issues until yesterday's update. These decks have video backgrounds in the masters, but the issue also happens on slides where there are still-image backgrounds or a simple color fill.

System:

Keynote 15.4 (7051.0.79)

MacBook Pro 16-inch, 2023, M2, 16 GB memory

macOS Tahoe 26.6.2

[Edited by Moderator]