After upgrading Jenkins 1.609.3 -> 1.625.1 without upgrading any plugins when I tried to run the slave from the web page the JNLP started and failed with connection refused.

I had to revert the upgrade and did not capture the exception logs. I will create a new testing Jenkins to recreate the problem and post more information later. This is incomplete post is to have an issue number to connect to the community feedback for the changelog as soon as possible.

Reverse proxy is set up in following way (relevant part of configuration with server name replaced):

ProxyRequests Off
ProxyPreserveHost On
AllowEncodedSlashes NoDecode

ProxyPass /jenkins http://my.host.cz:8080/jenkins nocanon
ProxyPassReverse /jenkins http://my.host.cz:8080/jenkins

Substitute "s|http://my.host.cz:8080/jenkins|/jenkins|iq"
SetOutputFilter INFLATE;SUBSTITUTE;DEFLATE

<LocationMatch "^/jenkins(?:/static/|/cli/|/git/|/jnlpJars/).*$">
AuthType None
</LocationMatch>

<LocationMatch "^/jenkins(??!/static/|/cli/|/git/|/jnlpJars/).)*$">

AuthName "Jenkins NTLM - Login using your DOMAIN username and password"
AuthType SSPI
SSPIAuth On
SSPIAuthoritative On
require valid-user

RequestHeader unset X-Forwarded-User
RewriteEngine On
RewriteCond %

Unknown macro: {LA-U}

(.+)
RewriteRule .* - [E=RU:%1,NS]
RequestHeader set X-Forwarded-User %

Unknown macro: {RU}

e
</LocationMatch>