Hast du auch eine Proxy Regel für die API gesetzt?
Sollte so aussehen laut Doku:
<VirtualHost *:443>
ServerName home.example.org
ProxyPreserveHost On
ProxyRequests off
ProxyPass /api/websocket ws://localhost:8123/api/websocket
ProxyPassReverse /api/websocket ws://localhost:8123/api/websocket
ProxyPass / http://localhost:8123/
ProxyPassReverse / http://localhost:8123/
RewriteEngine on
RewriteCond %{HTTP:Upgrade} =websocket [NC]
RewriteRule /(.*) ws://localhost:8123/$1 [P,L]
RewriteCond %{HTTP:Upgrade} !=websocket [NC]
RewriteRule /(.*) http://localhost:8123/$1 [P,L]
</VirtualHost>