Session Replay - Not captured for every client

[orchidee]

Just a question, given we depend on session replays heavily for troubleshooting purposes. I have observed intermittently, Dynatrace does not capture a session replay, if for example, user is using VPN or an external client blocks the persistent cookie. I cannot tell if the external client is really a VON user, but at end of day, Dynatrace is not capturing every single client's journey. What can cause this? For example, is this a delay relevant scenario capturing certain data from our application? 

Has anyone experienced this?

[t_pawlak]

Hi,
There are several reasons why Session Replay is not captured for every user, and what you describe (VPN users, cookie blocking, external clients) fits the typical root causes. Session Replay recording requires multiple technical conditions to be fulfilled in the browser, and when even one of them fails, the replay won’t start.
1. If the browser blocks cookies, scripts, or uses aggressive privacy settings (Safari ITP, Brave, some VPN proxies), the RUM JavaScript may not load correctly.

To verify:
Check that both JS agents load in Network tab:

ruxitagentjs_*Q*.js
ruxitagentjs_*D*.js

Ensure the script isn't replaced with an empty payload (some proxies do this).

2. Session Replay beacons blocked 

Session Replay uses binary POST beacons (rb_bf) with Content-Type: application/octet-stream.

Many systems block these:

• WAFs
• Firewalls
• Proxies
• VPN gateways
• Load balancers

If the beacon can’t be sent (or returns non-200), the replay never gets uploaded.
3. Client browser limitations. 
I mean several technologies prevent recording

4. IFrame restrictions

If an IFrame doesn’t have the RUM script injected, replay will be incomplete or not recorded at all.

5. Network / performance limits

Session Replay sends ~100 KB per minute of binary data.

Here you have some community/documentation links:
Session-replay-restrictions-web 
Initial troubleshooting when Session Replay is not available 
When session is not recorded, what we should check on the browser? 
Problem with sessions, not all sessions are being recorded in Dynatrace 

[orchidee]

Thank you for this feedback with details as to why this is happening. To also share, we do not use OneAgent. What happens is that our script captures certain data fields from the app before triggering the Dynatrace JS script. If a field is blank, the script fails one time, so the JS script is not triggered, therefore nothing is captured. 

Your items 1-5, any can relate to what you shared as could be different use cases, We are going to attempt a delay before capturing the data fields as may be a slowness scenario but do not know. Going to rule that out.

Do you think this may be the case?

[t_pawlak]

Yes — based on what you describe, this absolutely can be the root cause.

If your own script collects values before triggering the Dynatrace RUM JavaScript, and the script fails (for example, because a field is empty, null, or hasn’t been rendered yet), then:

• the Dynatrace agent is never initialized
• no cookies are created
• no Session Replay recording is started
• and no RUM beacons (rd_, rb_) are sent

In other words:
if your script throws even a single error before calling the Dynatrace bootstrapping code, Session Replay will not start at all.