after upgrade to nginx 1.16.0, $realpath_root returns incorrect path ?

[PGNet Dev]

after upgrading my working nginx instance from v1.15.x to

	nginx -V
		nginx version: nginx/1.16.0 (local build)
		built with OpenSSL 1.1.1b  26 Feb 2019
		...

running with php-fpm from

	php -v
		PHP 7.3.6-dev (cli) (built: Apr 23 2019 19:34:32) ( NTS )
		Copyright (c) 1997-2018 The PHP Group
		Zend Engine v3.3.6-dev, Copyright (c) 1998-2018 Zend Technologies
		    with Zend OPcache v7.3.6-dev, Copyright (c) 1999-2018, by Zend Technologies

my local site's no longer accessible.

standard log reports,

	2019/05/04 07:51:50 [error] 6510#6510: *8 FastCGI sent in stderr: "Primary script unknown" while reading response header from upstream, client: 127.0.0.1, server: dev01.pgnd.loc, request: "GET / HTTP/1.1", upstream: "fastcgi://unix:/run/php-fpm.sock:", host: "dev01.pgnd.loc"

in my config, I've got -- as usual,

	fastcgi_param SCRIPT_FILENAME  $realpath_root$fastcgi_script_name;

and my expected/target index.php is in its usual path

	/srv/www/test03/public/index.php

but turning on debug,

	2019/05/04 07:51:50 [debug] 6510#6510: *8 http script var: "/index.php"
	2019/05/04 07:51:50 [debug] 6510#6510: *8 fastcgi param: "SCRIPT_FILENAME: /usr/local/html/index.php"

the SCRIPT_FILENAME path is incorrect.  there appears to be an issue with $realpath_root.

While I'm digging locally for the problem ... question(s):

-- has anything changed in usage of $realpath_root?
-- are there any php v7.3.6 related issues?
-- any other hints?