Hi @Aaron_Reynolds_
To fix this I will recommend the following steps:
Step 1: Take them out as a read only user on the interface and resend them the email so they can access the interface again. You can do this on the screenshot 'Invite' and click 'Manage access'.
Step 2: Make sure they understand that all interfaces that are shared are not located in the 'All Workspaces' tap and you have to click 'Home' instead.
Step 3: Repeat for any other interfaces you have shared with them.
I have included screenshots below so you/they can understand where the interfaces should be located!
I hope this now fixes the problem 👌
Note: the screenshot 'Invite' shows how to invite them via email. 'Workspaces' shows the interfaces are not located there. 'Home' shows where the interfaces are shared.