Description:
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After a period of normal operation, $_POST 'disappears' and isset() returns false. Restarting Apache instantly restores normal operation. The same has occurred with $_COOKIE, $_REQUEST, and $_SERVER, but not at the same time as $_POST. This has happened on different servers at different sites running the same PHP code. Occurrence frequency varies a lot, but can occur as little as a couple of hours after restart. There are no resource limitations and everything else appears normal. None of my code modifies the superglobals, only reads single array elements into other named variables. Apache version is 2.4.35.

Test script:
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print_r($_POST);
// Normal operation - prints Array() 
// After fault appears - prints nothing

isset($_POST);
// Normal operation - returns TRUE
// After fault appears - returns FALSE