Dynamics NAV 2016 web client shows a blank page and a 500 error

Hi everyone, nav
we have the following problem, the Dynamics NAV 2016 web client shows a blank page.
The architecture is the following there is an azure server for users to remote connect there they should access (for training and test reasons) the windows client and the web client.
The web server is staged on server x1 and the nav application server is on server x2.
All prerequisites are installed,delegations have been done,application pool of nav web site and user for nav server is a domain user with necessary privileges.
Windows client is working normally everywhere.
Web client is working for some users,in others it gives a blank page.If a user deletes browsing history and cache of the browser then automatically get the blank page.
When checking the page with Fiddler it gives a 500 Internal Server Error. in the get of http://x1:8080/DynamicsNAV90/WebClient/Resources/desktop.css?h=ED980CB538B69B7B6C770A412D286FEF1DDC5870C6695F0CA5BEDDAA4EEFA121
Microsoft in the troubleshooting of the web client hasn't anything similar.
Any thoughts suggestions are welcomed
Kind regards