Sitemap_post1.xml is missing

https://www.ereviewbuy.com/post-sitemap1.xml

I don’t why it showing error 500 because it show when Google & also desktop Browser have not access to the file, there will be 2 possibilities,
1) either sitemap not created
2) or file had not accessed
, while other site maps working well for google

https://www.ereviewbuy.com/post-sitemap2.xml
https://www.ereviewbuy.com/page-sitemap.xml https://www.ereviewbuy.com/attachment-sitemap.xml
https://www.ereviewbuy.com/category-sitemap.xml
https://www.ereviewbuy.com/post_tag-sitemap.xml

Note I had 3200+ posts, I created 3000 limits mean in post_sitemap1.xml had 3000, & Post_sitemap2.xml had 200
Please give some tips to resolve it…

Thanks in Advance

Amazing -> When I returned back 1000, per sitemap it work fine again