unknown issue

Hello,
I don’t know why I have some problem with a site I am working on, at the top of the pages there is this error message.
This is not the first time this type of messages have appeared to me, I’m afraid it’s my fault, because these problems started showing up after I reinstalled the theme about a month ago, not caring about the wordpress warning message that it warned me that the theme had been updated and that I was therefore installing a previous version, I then solved the problem thanks to you but apparently not for everything.
So please look at the private content to be able to access.

Thanks and best regards