Can't access dashboard, WPMUdev website extremely slow

I've tried out a backup restoration with Snapshot. However, when I login and try to activate the plugins, starting with WPMU DEV Dashboard, I can't access the WPMU Dashboard. The error message is: "Your server had a problem connecting to WPMU DEV: "Error unserializing remote response.". Please try again.
If this problem continues, please contact your host with this error message and ask:
"Is php on my server properly configured to be able to contact https://premium.wpmudev.org/api/dashboard/v1/ with a POST HTTP request via fsockopen or CURL?"""

Server settings haven't been changed. I'm on shared hosting anyway.

I've also noticed that the WPMUdev website is extremely slow. Is there a problem with the website, so I can't login from my Dashboard?