When isolating using GRM Chinese symbols are not being displayed properly. In some cases characters may be replaced with empty square shapes, with bold lines on top and bottom.
Grid Rendering Mode (GRM) hides Document Object Model (DOM) elements and CSS from the client. It displays the browser content as images to the client. This method of content rendering does not support languages with multi-byte characters.
Examples: Chinese, Japanese, Korean
Use Vector Rendering (VRM) in your Isolation policy. What's inferred in the Admin Guide is that VRM is for more general use, and GRM is for special case scenarios.
VRM doesn't render characters the same way as GRM. It just presents the characters to the client as is, therefore, it doesn't not have rendering issues with multibyte characters. On occasion GRM will present multibyte characters properly, but if it's not then you should use VRM instead to solve the problem.