On the condition of a existing text field with “(backslash)n” inputted,
When I get a value of the field above via get_field() or get_post_meta(),
the value is “(backslash)n” as inputted.
But when I get a value of the field via ‘acf/validate_value’,
the value is “(backslash)(backslash)n”.
When validating values you need to take the backslashes into account. No it is not happening only to you, but is the way that the values are passed. This can be caused by your php installation and the “Magic Quotes” setting.