Do you know? Your sitemap should not larger than 10MB and should not contains more than 50,000 URLs because if is larger than these limits then this error can be generated,
critical sitemap error Too many sitemaps in index file
Divide your more than 50,000 URLs into multiple sitemaps then upload your each sitemap and also resubmit each sitemap to Google. A finest sitemap index file should contains 1000 URLs and must not exceed 10MB file size. You also can use Gzip to compress your sitemap file size.