Linked Accounts Don't Show under My Account

I have linked 2 other Business accounts to our main account several months ago, yet only the primary account shows under My Account.
When I try to link again I get this error:
"The account number you entered already exists in My Account. Only Accounts that have not been previously set up on My Account may be linked."
This suggests that they are in fact linked. Just not showing in the web portal.
Please assist.