Microsoft Teams display's "We're sorry – we've run into an issue." Similar to the image below
Exit out of Teams completely. Within the notification task tray find the Teams icon, right-click on the icon and select Quit or Exit
Click on the File Explorer icon
Within the location bar, copy and paste the below and press Enter
It should look like the below and "C:\Users\YOUR USERNAME\AppData\Roaming\Microsoft\Teams" will be in the address bar
Within the folder, just click anywhere then press CTRL + A (press and hold CTRL then press A) to select everything as show above.
Now right-click any one of the folders and select 'Delete'. Everything within that location/folder should now be deleted.
Open Teams and the issue should resolved. If you are prompted to Sign In, then Sign In using your school email address, i.e your firstname.lastname@example.org