I have tested your sitemap file on onlinecurl.com but I am still getting a HIT for cache which may be interfering with this.
Please get in touch with your host so that they can help in bypassing the sitemap file on the cache.
For testing, I disabled Rank Math’s sitemap module and installed the popular Google XMl Sitemaps plugin.
Unfortunately, it gives the same results:
That means the issue isn’t limited to Rank Math.
Personally, I think the issue is stemming from CloudFlare. We have seen so many users face the same issue and the only thing common it seems is the use of CloudFlare. Please disable that temporarily and see if that fixes the issue.