So yeah, do you mean WP user profile page?
There are a few other names that have the same result I usually paste in the first string of their smtp email address before the @ integer into the TO field, to find the recipient (if it does not find them the normal way by typing in variants of their full names) and that always works.
You thinking that there maybe a white space at the beginning or end of the name as I did try that in the TO box too.
I have all the members WP ID’s set as their email address (first string before the @) to help them remember their ID’s easily, but their Full First and Second Names are always set correctly.
screen shot attached of the members WP profile entry (Margaret Argent).
Hope this helps