Nuxt Fatal Error. Error: Invalid character in string

[kovan]

Somehow the description of a <video> entry in the sitemap has weird characters which seem not to be in the range allowed by the XML specification.

Here is the stack trace:

at XMLStringifier.assertLegalChar (node_modules/xmlbuilder/lib/XMLStringifier.js:208:19)
at XMLStringifier.cdata (node_modules/xmlbuilder/lib/XMLStringifier.js:61:21)
at new XMLCData (node_modules/xmlbuilder/lib/XMLCData.js:21:35)
at XMLElement.cdata (node_modules/xmlbuilder/lib/XMLNode.js:318:17)
at SitemapItem.buildVideoElement (node_modules/sitemap/dist/lib/sitemap-item.js:79:47)
at Array.forEach ()
at SitemapItem.buildXML (node_modules/sitemap/dist/lib/sitemap-item.js:173:28)
at Sitemap.toString (node_modules/sitemap/dist/lib/sitemap.js:280:62)
at Sitemap.toXML (node_modules/sitemap/dist/lib/sitemap.js:147:21)
at generateSitemap (node_modules/@nuxtjs/sitemap/lib/generator.js:58:42)
at async generateSitemaps (node_modules/@nuxtjs/sitemap/lib/generator.js:32:5)
at async Promise.all (index 0)
at async node_modules/@nuxtjs/sitemap/lib/module.js:44:5
at async Nuxt.callHook (node_modules/hable/dist/hable.js:1:959)
at async Generator.generate (node_modules/@nuxt/generator/dist/generator.js:91:5)
at async generate$1 (node_modules/@nuxt/cli/dist/cli-generate.js:46:22)

Weirdly , the error always ends says the conflicting character is at the last position of the string, tested with different strings. So I don't know which character is causing problems.

I have tried removing conflicting characters (using this code), but the error persists.

And this is the code that generates the entry, which has been working fine for quite a long time until this issue appeared.
Nothing really special about it I think:

function videoToSitemapEntry(video) {
    // Reference:
    // https://developers.google.com/search/docs/advanced/sitemaps/video-sitemaps
    let json = {
        url: `/video/${video.videosdb.slug}`,
        video: [
            {
                thumbnail_loc: video.snippet.thumbnails.medium.url,
                title: video.snippet.title,
                description: video.snippet.description
                    ? removeXMLInvalidChars(video.snippet.description, true).substring(0, 2040)
                    : video.snippet.title,
                duration: video.videosdb.durationSeconds,
                publication_date: dateToISO(video.snippet.publishedAt)
            },
        ],
        priority: 1.0,
    }
    return json
}

Help appreciated.

Thank you for your time.