diagnosing-missing-recordings（诊断丢失的录音）

Diagnosing missing session recordings

When a user asks "why wasn't this session recorded?" or "why don't I have any recordings?", follow this workflow to systematically diagnose the cause.

Available tools

Diagnostic signals

The PostHog SDK emits diagnostic properties on every event that explain the recording state. See the diagnostic signals reference for the full list.

The key signals are:

• $has_recording — whether PostHog has a stored recording for this session
• $recording_status — SDK state: active, buffering, disabled, sampled, paused
• $session_recording_start_reason — why recording started or didn't
• $sdk_debug_recording_script_not_loaded — recorder script blocked (ad blocker)
• $sdk_debug_replay_*_trigger_status — trigger states (URL, event, linked flag)
• $replay_sample_rate — configured sample rate at capture time

Workflow

Step 1 — Check if the recording exists

If the user provides a session ID, first check whether a recording actually exists:

posthog:session-recording-get
{
  "id": "<session_id>"
}

If this returns data, the recording exists — the issue is likely UI/filtering, not capture. If it returns 404, proceed to diagnose why.

Step 2 — Query diagnostic signals from events

Query the most recent event for the session to get SDK diagnostic properties:

posthog:execute-sql
SELECT
    properties.$has_recording AS has_recording,
    properties.$recording_status AS recording_status,
    properties.$session_recording_start_reason AS start_reason,
    properties.$sdk_debug_recording_script_not_loaded AS script_not_loaded,
    properties.$sdk_debug_replay_url_trigger_status AS url_trigger,
    properties.$sdk_debug_replay_event_trigger_status AS event_trigger,
    properties.$sdk_debug_replay_linked_flag_trigger_status AS flag_trigger,
    properties.$replay_sample_rate AS sample_rate,
    properties.$sdk_debug_replay_internal_buffer_length AS buffer_length,
    properties.$sdk_debug_replay_flushed_size AS flushed_size,
    properties.$lib AS sdk_library,
    properties.$lib_version AS sdk_version
FROM events
WHERE $session_id = '<session_id>'
ORDER BY timestamp DESC
LIMIT 1

Step 3 — Diagnose the verdict

Use the diagnosis logic reference to interpret the signals. The verdicts in priority order:

1. Recording exists ($has_recording = true) — recording is captured, issue is elsewhere
2. Ad blocked (script) ($sdk_debug_recording_script_not_loaded = true) — browser extension blocking the recorder script from loading
3. Disabled ($recording_status = 'disabled') — replay turned off in settings or SDK config
4. Trigger pending (trigger statuses are trigger_pending, none matched) — recording gated on trigger that never fired
5. Sampled out ($session_recording_start_reason = 'sampled_out') — excluded by sample rate
6. Buffering empty ($recording_status = 'buffering', buffer length = 0, nothing flushed) — initialized but no snapshots produced
7. Flush blocked (buffer length climbs across events while flushed_size stays at 0) — snapshots are produced but the /s/ ingestion endpoint is blocked by an ad blocker or misconfigured reverse proxy. Detecting this requires querying the trend across the session's events — see example 3 in examples.md
8. Unknown — signals don't match a known pattern

Step 4 — Check project-level settings (if no session ID)

When the user asks about recordings missing project-wide (no specific session), query for recent sessions to check the pattern:

posthog:execute-sql
SELECT
    $session_id,
    properties.$recording_status AS recording_status,
    properties.$session_recording_start_reason AS start_reason,
    properties.$sdk_debug_recording_script_not_loaded AS script_not_loaded,
    properties.$replay_sample_rate AS sample_rate
FROM events
WHERE event = '$pageview'
    AND timestamp > now() - INTERVAL 1 DAY
GROUP BY
    $session_id,
    recording_status,
    start_reason,
    script_not_loaded,
    sample_rate
ORDER BY max(timestamp) DESC
LIMIT 10

Look for patterns:

• All disabled → replay is turned off in project settings
• All sampled_out with low sample rate → sample rate too aggressive
• All script_not_loaded → likely a CSP or deployment issue, not just one user's ad blocker
• Mix of statuses → per-session issue, dig into specifics

Step 5 — Provide actionable recommendations

Based on the verdict, recommend specific actions:

Examples

See real-world diagnostic examples showing how signal combinations map to verdicts. Use these to calibrate your interpretation of query results.

Tips

• If $lib_version is very old, some diagnostic signals won't be present. Note this to the user — upgrading the SDK will provide better diagnostics.
• A session might have events but no recording if the recording was deleted due to retention. Check the session's timestamp against the project's retention period.
• If $has_recording is true but the user can't find it, check if it's filtered out by duration, activity threshold, or playlist filters.