Bug: Canvas content missing or disappears during session replay (Flutter web & raw canvas)

[ordehi]

Bug Description

Bug description

Session replays involving <canvas> elements are either partially or entirely blank during playback, especially after scrubbing. This affects both:

1. Raw HTML canvas content
2. Flutter web apps (which render entirely in canvas)

Observed behaviors:

• The canvas content renders correctly at first, but disappears entirely when scrubbing backward or forward on the timeline.
• In some recordings, the canvas never renders at all — the replay remains blank except for any non-canvas DOM elements.
• In Flutter-based examples, some sessions behave similarly (canvas visible at first then disappears), while others are blank from the start.

Some flutter examples where it's particularly bad:

• https://us.posthog.com/project/184840/replay/0197dc89-8e08-7fc6-99ec-72c4cbb707c1?t=809
• https://us.posthog.com/project/184840/replay/0197faa4-bb3d-7d29-b253-8cf8f08afa9e?t=148

Plain canvas:

• https://us.posthog.com/project/150522/replay/019819c8-bb7c-7f76-b36d-86f43b566c88

How to reproduce

Minimum reproducible example: https://gist.github.com/ordehi/209b73fe30b5779e07344f45f4c3c6ed

1. Create a page that renders all content using a <canvas> element (e.g. a simple animation)
2. Enable canvas recording in project settings
3. Record a session that includes canvas rendering
4. Play the session in PostHog, and scrub the timeline backward

Expected: Canvas state is restored correctly at all points in the timeline
Actual: Canvas content disappears or fails to render entirely

Additional context

From: https://posthoghelp.zendesk.com/agent/tickets/34275

Debug info

Kind: support

Target area: session_replay

Report event: http://go/ticketByUUID/28af40f7-7fe0-4a03-8de6-4d28128fec84

Session: https://us.posthog.com/project/sTMFPsFhdP1Ssg/replay/01980e63-3408-7039-8d24-c2d1db6b48cd?t=1043

Exceptions: https://us.posthog.com/project/2/error_tracking?filterGroup=%7B%22type%22%3A%22AND%22%2C%22values%22%3A%5B%7B%22type%22%3A%22AND%22%2C%22values%22%3A%5B%7B%22key%22%3A%22%24session_id%22%2C%22value%22%3A%5B%2201980e63-3408-7039-8d24-c2d1db6b48cd%22%5D%2C%22operator%22%3A%22exact%22%2C%22type%22%3A%22event%22%7D%5D%7D%5D%7D

Location: https://us.posthog.com/project/184840/replay/0197faa4-bb3d-7d29-b253-8cf8f08afa9e?t=148

Persons-on-events mode for project: person_id_override_properties_on_events