ClassicPress 1.7.2 cannot enable sitemap

Introduction to the running environment

ClassicPress version: 1.7.2
PHP version: 8.0, 8.1
Database: planetscale
XML Sitemap Generator for Google: 4.1.19

Problem description

I switched from WordPress to ClassicPress (1.6.5) in October 2023 and installed the XML Sitemap Generator for Google plugin. It was working fine until yesterday, when I suddenly noticed that the sitemap had disappeared. I went to the ClassicPress Settings and under Reading, I found that XML Sitemap Index was not checked to enable it. I checked XML Sitemap Index and saved it, but the page automatically refreshed and I found that the XML Sitemap Index that I had just enabled had disappeared. I repeated this several times with the same result.

Summary

OptionCan changes be saved?DescriptionXML Sitemap IndexChanges cannot be savedCheckbox disappears after saving and refreshingGoogle News SitemapChanges cannot be savedCheckbox disappears after saving and refreshingAdditional robots.txt rulesChanges can be savedContent can be saved

https://github.com/RavanH/xml-sitemap-feed/issues/46

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