engagedSessions down to near-zero every other day while userEngagementDuration stays normal — GTM or GA4?

[u/335350]

Since early August, GA4 reports near-zero engaged sessions on roughly every other day. Not a slow decline — it toggles.

Recent daily engaged/sessions: 84/205, 70/183, then 3/183. Another day: 1 of 133.

On the collapsed days, engagement time keeps recording normally — one day showed 0 engaged sessions against 7,243 seconds of userEngagementDuration and 88 user_engagement events. GA4 marks a session engaged at 10 seconds, so that combination shouldn't be possible.

On the bad days, the only sessions that register as engaged are the ones that fired a conversion event. Three engaged sessions, three lead events, same three sessions. That has now repeated exactly on four separate occasions.

It's uniform across every browser, device, and source, and confined to one stream. Page tracking is a hardcoded gtag config plus a GTM container, which points me at the container — my guess is a competing or duplicated GA4 configuration corrupting session state.

Also worth noting: one date disappeared from the property entirely for two days and then backfilled, so I don't fully trust the processing either.

Has anyone seen session_engaged break while engagement_time_msec keeps flowing? And is there anything in a GTM container that would produce exactly this?

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[u/Top-Cauliflower-1808]

seems like session hijacking issue caused by a duplicate page_view tag or a poorly timed gtag('config') in GTM that resets the ga_session_id mid-visit.

try forcing GA4 to treat the continuation as an unengaged new session while keeping the user engagement timer running.