As per this post (http://www.isfdb.org/wiki/index.php/ISFDB:Moderator_noticeboard#Mikael_Bourgouin_.3D.3E_Mika.C3.ABl_Bourgouin) on the Moderator Noticeboard:
"I had to change [Mikael Bourgouin] to "Mikaal Bourgouin", variant that to "Mikaël Bourgouin", then correct the variant spelling back to "Mikael Bourgouin". This means that "Mikael Bourgouin" and "Mikaël Bourgouin" now exist simultaneously in the database.
The existence of two author names which are near-identical except for a character which collates the same way as another character in Latin-1 creates a problem when the software needs to determine which author ID to use. "Edit Author" should not let editors create these types of author pairs.
Anonymous
Fixed in common/authorClass.py, installed in SVN 795 on 2021-11-02. Closing the Bug report.