The following update in the specification was introduced in 1.05.03

Opc UA Part 3 1.04 / 8.32 String
This Built-in DataType defines a Unicode character string that should exclude control characters
that are not whitespaces.

Opc UA Part 3 1.05.04 / 8.31 String
This Built-in DataType defines a Unicode character string that should exclude control characters. Unicode control characters are defined by Unicode C0 and Unicode C1

This a breaking change and would not allow white space charters or multi line strings, because '\t' (tab), '\n' (line feed), '\r' (carriage return) are part of Unicode C0.

This change was not mentioned in the Revision 1.05.03 Highlights. It seems like this was changed by mistake.
The only related mention is this:
"The CONTROL Characters not Allowed in NodeIds, QualifiedNames and ExpandedNodeIds." https://mantis.opcfoundation.org/view.php?id=9163