(Thank you for providing an open source solution of Rich Snippets)

File

breadcrumbs.phtml#L36

Reproduce

Create a category and let its name contains " or \.

Output(invalid JSON):

{
    ...
    "item": {
        "@id": "",
        "name": "Some\Category\Name"
    }
    ...
}

Expected result

" or \ should be escaped to \" or \\