After upgrading to GW 18 SP1 our WebAccess servers behave unusual.

There are 5 webaccess servers and there is an apache load balancer in front of them.
The number of logged in users on webacc1 is about 300 and the number of apache requests currently processed is about 850. Almost all of the requests are similar like this:
"GET /gw/webacc/poll?User.context=b19a618dc5182221e9472fe787a9fc"
The apache requsest are in W which means "Sending Reply". The b19a618dc5182221e9472fe787a9fc string is listed multiple times (up to 8 times) ATM.
Apache error log is full with
"Error reading from remote server returned by /gw/webacc/poll" and "The timeout specified has expired: proxy: error reading status line from remote server localhost:18080"
Is this normal?
IMHO, if there are 300 logged in users, then no more than 300 apache requests should be there. One active user should have one active apache request.