Able to chat with some guest accounts and not others

We have two guest accounts, both people from the same external organization. Lets call them Jane Doe and John Smith from contoso.com. If I open a new chat and type Jane Doe, Teams finds her guest account and offers Jane Doe (Guest) as the match for the name, and all works fine. If I type John Smith, it does not find him. If I enter John Smith's email address johns(at)contoso.com it is able to open a chat, but lists him as John Smith (External) and of course the options for the chat are restricted (can't add a new tab for example). I do not see any settings differences between the two accounts, both guest accounts were created by the invitation method. The biggest difference is that Jane's account is about 4 yrs old, where John's is only 1 week old.