I have the same problem with other labs, by the way.
Things I would try…
Does clicking reconnect work?
If you are using a VPN product, disable it when using the labs.
If you are using Firefox try a clean install of Chrome, and if you are using Chrome, try a clean install of Firefox. The idea is to try a browser clean of any plugins or alterations.
If you are using a shared wireless connection, try to access the labs when usage is light. If you have a chance to use a wired connection please try it. Trying to run labs over a public shared connection is not a good idea.
If you have an AV product installed try disabling it and then accessing the lab.
I’m not saying these things are the fix, but they work a lot of the time, and they are worth trying.
Thank you very much, it actually worked with Firefox! Do you perhaps have any idea what the problem might have been with Chrome, why it didn’t work there, and what I can do to change this (so that I can also use Cybrary with Chrome)?
I would disable all Chrome extensions to start, if that works you can re-enable them one by one until you find the culprit.