I can't see my trainee after their ESR was signed off?

If you can't see the link to the trainee from the dashboard on the right hand side then instead click through to the Supervisor dashboard as they should be listed there:

If they are still not listed it may be that the trainee themselves can link you: My supervisor can't see my portfolio / Changing my supervisor or failing that if you contact your local training programme they should be able to fix this.