After looking at the code for elementor pro it is my guess that the code in elementor pro that gets the value of the field is being called before ACF is initialized. This guess is also based on the fact that a recent change in ACF that prevents the retrieval of values before ACF is initialized and this was done to prevent the use of fields in ACF that are not created using ACF. This means that any call to ACF before the hook ‘acf/init’ is called will return an empty value.
But again, this is only a guess, and because you are using elementor pro I really don’t know how to figure it out.
Do you have any custom PHP code added to this site outside of the plugins mentioned that could be called?
I would start by looking at the HTML output directly before the error and try to figure out where output is created.
