How Dynatrace decides which synthetic sessions to show?

[deni]

Hi,

We have the following case:

1. Session sampling for app is 100% (all sessions should be captured)

2. Synthetic monitor which tests this app every 5 minutes.

There are days where almost all of the synthetic sessions are there, but in the last 3 days there are only 2 or 3 session per day. I searched in the documentation, but couldn't find anything about how Daynatrace decides which sessions to show and which not.

Can you help me with that? I'm I missing something from the official documentation?

Thanks!

Regards, Deni

[HannahM]

There are some troubleshooting steps for this here.  

[deni]

Hi @HannahM ,

Thank you for sharing the link. I’ve reviewed it, but it seems to cover cases where browser monitors are automatically assigned to applications. In my scenario, synthetic sessions are visible, but most of them are missing, so I don’t think this applies.

To summarize my case:

• Session sampling for the application is 100% (all sessions should be captured).

• A synthetic monitor tests this application every 5 minutes.

• On most days, almost all synthetic sessions appear, but in the last three days, only 2–3 sessions per day are visible.

I haven’t found anything in the official documentation explaining why some synthetic sessions are not shown, even with full session sampling.

Regards, Deni

[p_devulapalli]

@deni Do you mean to say synthetic sessions are visible but only the replay is missing or  the session itself is not being executed?

Is this a private synthetic location ?

https://docs.dynatrace.com/docs/shortlink/synthetic-calculations#why-monitors-dont-run

[deni]

@p_devulapalli

It's a public location synthetic monitor that tests login and performs several clicks on a website. The monitor executions occur every 5 minutes as expected, and the successful runs are visible in the monitor results.

However, in the Session view, only a few of those executions appear — the ones that are shown include the full session replay and related data.
The issue is that most of the synthetic sessions are missing, even though the monitor runs consistently at the defined schedule and session capture is set to 100%.

[HannahM · Accepted solution]

This is usually due to the RUM injection not being picked up by the Synthetic player, which is why automatically assigned applications are important. If you open a support ticket, they can check the logs for the Synthetic executions and see if the RUM injection was made before the Synthetic injection or if RUM was too late. If the RUM injection was after the Synthetic injection, then the session won't be linked to your application, and you should check the RUM injection rules, as it likely needs to be tweaked to inject earlier. 

[deni]

Hi @HannahM ,

Thanks a lot for your help!

I contacted Support, and they confirmed that the RUM configuration is being picked up by the Synthetic monitor but is missing some user actions.

Just wanted to share their feedback here as it might help others with a similar case.