Sitemap problem with Rankmath?

Hi, getting a issue with Rankmath plugin. The issue is, my sitemap keep vanishing. When it's vanished I just have to go to Rankmath » Sitemap » Save Changes that's it.

Now Sitemap will work fine for couple of days (7-20days) then it will again vanished and I've to get that information and again have to do Rankmath » Sitemap » Save Changes.

Please help me, I really love that plugin.