Thanks for reporting this issue.
Unfortunately we are not able to reproduce this issue. Could you kindly provide the following information to help us nail this down.
1) Kindly share both version of fonts at ShareWithAI@adobe.com .
2) Please mention the title of this issue as the subject of the mail with tag [UserVoice] and Uservoice link in subject of email.
An error occurred while saving the commentArt Grootfontein commented
I have the same bug using Fonstelf in Illustrator CC 24.3 on Mac OS 10.14.6 with kerning options :
When I change the kerning setting of a letter and click the "Install" button of the Fontself extension, the font is not updated in illustrator.