Internal server error when logged in

The login page looks fine.

When I login to my piwik it shows the Dashboard views but no data is shown. Instead a red error message is shown in each view. And if I refresh I get a blank page saying “An internal server error occurred. Please try again later.”.
Now, if I close the browser and open again, I can see the login page again without errors.

It has worked before, I don’t know why it suddently stopped.

Piwik version: 2.10
PHP 5.5.9
I’m using Pound as a load balancer / reverse proxy (https to http) - but I’m not experienced with proxies, so it could be something to do with this. I’ve followed the piwik guides to using proxy, but it didn’t help.

Here is the General section from config/config.ini.php. Salt, IP and Domain are removed.

proxy_client_headers[] = "HTTP_X_FORWARDED_FOR"
proxy_host_headers[] = "HTTP_X_FORWARDED_HOST"
salt = "[REMOVED]"
trusted_hosts[] = "[IP]"
trusted_hosts[] = "[DOMAIN]"
assume_secure_protocol = 1
force_ssl = 1

I solved this by upgrading to Piwik 2.11.1.

It seems this was the issue: Mysql process list is clogged with very inefficient updates on the archive blob tables · Issue #7195 · piwik/piwik · GitHub