Only registered leaders in the unit can see the unit roster, I believe.
A couple of questions:
Are the parents in questions current or former registered adults in any BSA capacity (e.g. leaders, merit badge counselors, etc), have they taken YPT, or did they register using the online form? Any one of these (definitely the first two and possibly the last one) will generate a BSA ID which may cause complications with login.
Are the parents logging in with their email addresses or their my.scouting logins?
When you look at the scouts’ accounts via the unit roster (My Dashboard -> My Units -> Unit Roster -> Scout’s name), and scroll to the scouts’ connections for these parents, do the parents show up with a little closed link next to their names as in the snapshot below, or is it a broken link?
When you then scroll down and click on “Scout’s name’s Connections” (snapshot below), do the parents show up as pending (second snapshot below)?
This might indicate that something happened when accepting the invitation to connect to their scouts, either on the user side or on the code side.
One possible workaround would be to go into the dashboard for each scout with the problematic parent connection (via the path I described above), click on the parents’ names, and inside the connection dialog that pops up, click on Update (don’t change anything). That might kick-start the system into recognizing the parent connection.
I don’t know if this is a problem that is occurring for a lot of other units, but I’m wondering if it’s better to report it to firstname.lastname@example.org before you do anything to “fix”/work-around the issue. That way, they could try to diagnose what’s going wrong before they fix it.