If students have lost points, lost data, not seeing tasks, this could be as a result of having more than one account and being logged in to the wrong one.
If you suspect this:
- check your Admin page and that they are registered in your class
- check that they are logging on using the username/email that is registered in your class on the Admin page.
- check that their points seem sensible and they haven't created a new account.
- check that their name doesn't appear twice in the Admin section. If it does, remove the inactive one and ensure they log on using the username of the active account.
- test if there's a second account by trying to add them to your class.
Here's more on duplicate student accounts.