500 Code in Apache log because of Websocket

Hello everyone

I just upgraded Mattermost to the version 3.0.2. It works all fine only that I see in the apache log this:

[23/May/2016:17:56:18 +0200] "GET /api/v3/users/websocket HTTP/1.1" 500

Here is the relevant configuration of my apache:

RewriteEngine On

RewriteCond %{REQUEST_URI} ^/api/v3/users/websocket [NC,OR]
RewriteCond %{HTTP:UPGRADE} ^Websocket$ [NC,OR]
RewriteCond %{HTTP:CONNECTION} ^Upgrade$ [NC]
RewriteRule .* ws://xxxx:8065%{REQUEST_URI} [P,QSA,L]

RewriteCond %{DOCUMENT_ROOT}/%{REQUEST_FILENAME} !-f
RewriteRule .* http://xxxx:8065%{REQUEST_URI} [P,QSA,L]
RequestHeader set X-Forwarded-Proto "https"

Require all granted
ProxyPassReverse ws://xxxx:8065/api/v3/users/websocket
ProxyPassReverseCookieDomain xxxx:8065 xxxx

Require all granted
ProxyPassReverse http:/xxxx:8065/
ProxyPassReverseCookieDomain xxxx xxxx

I don't understand because Apache gives a 500 because i think Mattermost works fine like before. The only thing that I noticed is that the browser takes longer until it gets the status of the other users.

Thanks for your help