My problem is quite the same with version 3.9.1+build 20200814 and theme fordson 3.9.
Each time that I connect on administration, presentation, theme fordson, the following message (see picture of screen below) comes.
It appeared recently, it was not occuring when installing the site in june 2020.
Here is a picture of my screen : and clicking twice on ok, it disappears. I don't know if it has consequences on parameters that I would modify, will they be saved or not ? Has someone the same problem? On Edge or on Chrome, it is all the same. The same screen and problem occured also when saving a feedback to a student.... and then it was saved at the end.
Thanks for any help ! (I speak french, sorry for my poor English ;)