XML Sitemap and Robot TXT

Hi

My Sitemap goes blank and after deactivating WP Performance it starts showing again.

Although my https://excelnumber.com/robots.txt file is working fine. The problem is Google robots.txt Tester is throwing an Error. Please check the below image.

https://1drv.ms/u/s!AkC9mOZ_0x6OtBRgvWC78s1JDOzO?e=jWN1IL

Let me know your thoughts on this.

The page I need help with: [log in to see the link]