I hit what appears to be the same GC-sweep callback storm on Ubuntu
24.04 (gnome-shell 46.0-0ubuntu6~24.04.14, mutter
46.2-1ubuntu0.24.04.15, Wayland, fractional scaling, 4 monitors), with a
different user-visible consequence that may help pin down the mechanism:
permanently invisible windows.

Trigger: Chrome (native Wayland) was killed under memory pressure and
its session restore re-mapped ~60 windows in a burst. During the burst,
gnome-shell logged 1,077 "Attempting to call back into JSAPI during the
sweeping phase of GC ... blocked and the JS callback not invoked"
messages in ~7 seconds, with a signal roster nearly identical to comment
#2's (notify/window-entered-monitor/window-left-monitor on MetaDisplay,
size-changed on ShellWM, window-added on MetaWorkspace, ...) — plus 114x
"map on ShellWM".

The dropped `map` handlers are the interesting part: windowManager.js
_mapWindow() is what shows a newly mapped window's MetaWindowActor, so
each dropped map left a window permanently invisible — present in Alt-
Tab and rendered in the overview, absent from the desktop and from
screenshots. Exactly 57 windows were affected, matching 57x blocked
"kill-window-effects on ShellWM" (and 114 = 2x57 maps). Actor state on
every ghost: visible=false, opacity=255, scale=1, surface child healthy;
a bare actor.show() fully repairs each one.

This was with only the stock session extensions enabled (DING,
AppIndicators, Dock; the Extensions toggle was off, which doesn't
disable those three).

I can provide more information if that is useful.

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https://bugs.launchpad.net/bugs/2117116

Title:
  Display goes black, gnome-shell goes 100% CPU spamming "Attempting to
  call back into JSAPI during the sweeping phase of GC."

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