Connection to qlik engine failed for unespecific reasons with users logged via Keycloak

[MNGM]

Hi Team, 

We have several users accessing via Key-cloak (external clients). But with a group of them from a specific Client is receiving a message " Connection to Qlik Sense engine failed for Unspecific reasons". 

If I impersonate the users directly on Key-Cloak I can access Qlik and running apps without issues.

Could you please assist?

Thank you

[Gysbert_Wassenaar]

Is the fqdn of the qlik sense server that the users use in the url whitelisted in the virtual proxy that they're using?

And check that websocket connections are working and stable. Is there a http proxy involved between the users browsers and the Qlik Sense server? If so make sure it supports websockets properly and upgrades http connections as needed.