You should end up back on the Microsoft Stream web page:
You can try clearing all of your cookies in your browser. This would normally clear any login information or locally stored data that could be confusing Stream.
Instructions for a number of browsers can be found at https://us.norton.com/internetsecurity-privacy-how-to-clear-cookies.html
Make sure you are logged in to Office 365 with your University credentials. You can do this in several ways:
Office 365 homepage: https://www.office.com/
Outlook: https://outlook.office365.com/
Stream: https://web.microsoftstream.com/
You must be logged in with your university credentials rather than a personal account.
Your internet browser may be causing the issue.
Click the 3 dots in the top right of the page
Settings > Cookies and other site data
Turn on 'Allow all cookies'
Turn off 'Block third party cookies'
See also
https://support.google.com/chrome/answer/95647?co=GENIE.Platform%3DDesktop&hl=en
See Allow or block cookies
Select Allow all cookies
Click the 3 dots in the top right of the page
Settings > Site Permissions > Cookies and Site Data
See also
https://support.microsoft.com/en-gb/help/17442/windows-internet-explorer-delete-manage-cookies
Go to Safari menu
Select Preferences:
Untick Prevent cross-site-tracking
Finally if none of this does make things work if you are able to open your Browser's Developer Tools (typically Ctrl-Shift-I for Chrome, or the "Developer Tools" option):
and capture any thing that appears in Console
And send the details to help@strath.ac.uk with the details of the class, activity & ideally the video, then it really does give us more information to investigate the cause.