Error Sitemap is HTML

( Note: I searched forum here but got no solution.)
Hi,
I was having problem with yoast seo because it was putting a dash in front of my site title (Homepage). I disabled it and installed Google sitemap generator tool to solve this issue.So my sitemap address changed. After 6 hours i saw that all my rankings dropped. I was worried so i again installed yoast plugin and removed google sitemap generator. After few hours my rankings are back but i’m facing an error in google search console.My post sitemap has an error only.

My site address: https://topusmovies.com/
My Sitemap index: https://topusmovies.com/sitemap_index.xml (No error working fine)
https://topusmovies.com/post-sitemap.xml ( ERROR )
https://topusmovies.com/page-sitemap.xml (No error working fine)
https://topusmovies.com/category-sitemap.xml (No error working fine)
https://topusmovies.com/post_tag-sitemap.xml (No error working fine)

As you can see above only post-sitemap.xml has error only.
image 1 https://prnt.sc/cltiey
image 2 https://prnt.sc/cltiqm

According to yoast seo it is due to w3total cache so i disabled w3total cache but still it has a problem.

Note 1: My robots file is not blocking it.
Note 2: I tested map in search console> sitemaps but it tells me no error after test but error still exists.
See image 3 please https://prnt.sc/cltk8c

Note 3: I validated my site map in W3 validator but it is ok.
Note 4. I can fetch and render it and upon rendering it shows same sitemap for ROBOTS and USERS.
See Image 4 https://prnt.sc/cltm2s
see image below for http header response
Image 5 https://prnt.sc/cltmp3

Now Please some wordpress developer help me. I searched forum here but got no solution. If problem not solved my site will be deindexed in a few days.

Regards,
Muhammad Ahmed