can you try disabling all other plugins to check for a conflict.
Also if you have any custom functions or code inside a GP Hook Element also remove them to check for conflicts.
Currently I have given it to hosting provider as I have recently migrated to another hosting provider and the issue arrived after that. So, they are looking over it. If they don’t resolve it, I will try your method.
I’m not seeing that error, but I am seeing some broken HTML above the header. Maybe it’s a broken hook you’ve added? Or maybe some custom HTML added to the theme files?