inconsistency between the VM page visibility status and the visibility status of the page

Hi,

i had a issue here, When executing a SELECT statement using an index-only scan, i got a wrong row number because there may be an inconsistency between the VM page visibility status and the visibility status of the page,the VM bit is set and page-level is clear

i read the code and note that there has a chance to happen like this,but how it happens?

the code do clear the page-level visibility and vm bit at the same time, i don not understand how it happens