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Sorry to hear you’re facing problems 
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In order to help you as quickly as possible, before clicking Create Topic please provide as much of the below as you can. Feel free to use a pastebin service for logs, otherwise either indent short log examples with four spaces:
example
three backticks above a
Or for longer, usend below the code snippet:
longer
example
here
Some or all of the below information will be requested if it isn’t supplied; for fastest response please provide as much as you can 
Nextcloud version (eg, 12.0.2): 17.0.2
Operating system and version (eg, Ubuntu 17.04): 17.0.2
Apache or nginx version (eg, Apache 2.4.25): 2.4.
PHP version (eg, 7.1): 7.2
The issue you are facing:
I set up LDAP. Configuration is OK. Users show up.
When an LDAP User tries to log in it takes a long time, then the following error is shown:
Gateway Timeout
The gateway did not receive a timely response from the upstream server or application.
Is this the first time you’ve seen this error? (Y/N): Y
Steps to replicate it:
- Try to log in as an active directory user
The output of your Nextcloud log in Admin > Logging:
nothing is written in the log when the user tries to log on.
I have the same setup at another customer. The only difference is that the LDAP server is a windows server 2008 R2 there. It works without any problems there.
In this environment the LDAP server is windows server 2019 (active direcotry)
Firewall is disabled on the windows server.
Both VMs run on same hyper-V host.
What is different in Windows 2019 compared to 2008?
Thank you in advance