COOKIES DISABLED ERROR

Having a Vaadin web-app 7.6.2

When web-app is deployed on Tomcat http://localhost:8080//
Every thing works fine.

Even when deploying it to http://localhost:8080//UI/
by configuration:
@WebServlet(urlPatterns = {“/UI/", "/VAADIN/”}, name = “”, asyncSupported = true)
Every thing works fine.

But wen adding the Web-Server Apache and redirecting
http://localhost:8080//UI/
to
http://my_appserver.domain.de/

it returns COOKIES DISABLED

Apache config:
ProxyPass /VAADIN/ ajp://127.0.0.1:8009//VAADIN/
ProxyPass / ajp://127.0.0.1:8009//UI/
ProxyPassReverseCookiePath //UI/ /
ProxyPassReverseCookiePath //VAADIN/ /VAADIN/

PS: The Application works fine with no /UI/ subpath.

Have you checked the last comment of this discussion?

https://vaadin.com/forum#!/thread/3620992

Unfortunately this is some different case.
thread: 3620992
handles the situation, that some application is deployed at path /xxxx and should be reachable at path /yyyy via Apache

with application is deployed at path /xxxx and should be reachable at path / via Apache works

my case is
that the application is deployed at path /xxxx and is reachable at /xxxx/yyyy (by application config)
and should be reachable at path / via Apache

I have similar problem. Using Vaadin 7, and Firefox 67.
When I’m using Vaadin application in private mode, I don’t have this error.
Similarly, there’s no error in Chrome.