Problem with Sitemap

I have a problem on Google Search console reporting the sitemap of my site like this:

https://www.himaxcr.com/sitemap_index.xml == > Couldn’t fetch
Click on click on it, it shows: Sitemap could not be read

I read all previous cases and I’m not able to determine the root cause.

Please test the site map here: https://www.xml-sitemaps.com/validate-xml-sitemap.html

1) I installed Health Check & Troubleshooting plugin, and just enable Rank Math.
– Still the same error happened.

2) I’m using nginx and redis, so I added the string

# START Nginx Rewrites for Rank Math Sitemaps
rewrite ^/sitemap_index.xml$ /index.php?sitemap=1 last;
rewrite ^/([^/]+?)-sitemap([0-9]+)?.xml$ /index.php?sitemap=$1&sitemap_n=$2 last;
# END Nginx Rewrites for Rank Math Sitemaps

Just in case…, same issue is reported

3) I’m not using any other caching plugin, just redis at the server level, so I disable redis completely and still the same error happened, even though I flush all the cache with: redis-cli flushall

4) Just in case I doubled check what I’m excluding from redis and the sitemap is excluded:

# Don’t cache uris containing the following segments
if ($request_uri ~* “\?add-to-cart=|/cart/|/my-account/|/checkout/|/shop/checkout/|/wp-json/|/store/checkout/|/customer-dashboard/|/addons/|/wp-admin/|/xmlrpc.php|wp-.*.php|/feed/|index.php|sitemap(_index)?.xml”) {
set $skip_cache 1;
}

From a different server I can access the sitemap just fine and what’s really interesting is that it comes with the correct content type text/xml

[20:10][root@fbvstore001 conf.d]# curl -I https://www.himaxcr.com/sitemap_index.xml
HTTP/1.1 200 OK
Date: Fri, 12 Jun 2020 20:21:02 GMT
Content-Type: text/xml; charset=UTF-8
Connection: keep-alive
Set-Cookie: __cfduid=d54e3b1f6c7584c00bc079ae7c4f6becb1591993262; expires=Sun, 12-Jul-20 20:21:02 GMT; path=/; domain=.himaxcr.com; HttpOnly; SameSite=Lax; Secure
Vary: Accept-Encoding
X-Robots-Tag: noindex
Pragma: public
Cache-Control: maxage=31536000
Expires: Sat, 12 Jun 2021 20:21:02 GMT
X-Powered-By: centminmod
X-Cache: BYPASS
X-Cache-2: BYPASS
X-Frame-Options: SAMEORIGIN
X-Xss-Protection: 1; mode=block
X-Content-Type-Options: nosniff
CF-Cache-Status: DYNAMIC
cf-request-id: 034bca79840000ef1e15940200000001
Expect-CT: max-age=604800, report-uri=”https://report-uri.cloudflare.com/cdn-cgi/beacon/expect-ct”
Server: cloudflare
CF-RAY: 5a2646a26a9aef1e-MIA
alt-svc: h3-27=”:443″; ma=86400

I’m out of ideas, Google Search console is not able to use this sitemap.
Thank you,
Best Regards