SPEEDINDEX_OF_ZERO

I just made a few changes to the plugin but I run into the SPEEDINDEX_OF_ZERO message in PageSpeed Insights. Could you give me some help about it?

Speed ​​index
Error!
Chrome did not collect any screenshots when loading the page. Check that there is visible content on the page and try to run Lighthouse again. (SPEEDINDEX_OF_ZERO)

a cordial greeting

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