Thanks, @AmereyJustus! I'm sorry you are still having isssues, and these browsers do appear to be up to date. Although the Thinkpad should be fine, there could be some hardware issues or internet connection issues. Another idea at this point is to follow these best practices:
Close all applications, including background applications
Restart your computer
Make sure you are connected to a good internet source -- a wired connection is best, but sitting close to a router is good, too.
Make sure no other device sharing your internet connection is streaming video, facilitating online gaming, etc.
You can also contact Mastery Connect Support to log a case and investigate this further. I hope you can get this working!