Azure Multisite all pages redirect to wp-signup.php

Hey folks- I’m running into wp-signup.php redirect loop for all pages (admin, login, main site homepage). The server is MS Azure.

With a network set up:
define( 'WP_ALLOW_MULTISITE', true );

And the network configured:

define('MULTISITE', true);
define('SUBDOMAIN_INSTALL', true);
define('DOMAIN_CURRENT_SITE', 'pnasb.net');
define('PATH_CURRENT_SITE', '/');
define('SITE_ID_CURRENT_SITE', 1);
define('BLOG_ID_CURRENT_SITE', 1);

And the web.config configured:

<?xml version="1.0" encoding="UTF-8"?>
<configuration>
    <system.webServer>
        <rewrite>
            <rules>
                <rule name="WordPress Rule 1" stopProcessing="true">
                    <match url="^index\.php$" ignoreCase="false" />
                    <action type="None" />
                </rule>
                <rule name="WordPress Rule 2" stopProcessing="true">
                    <match url="^wp-admin$" ignoreCase="false" />
                    <action type="Redirect" url="wp-admin/" redirectType="Permanent" />
                </rule>
                <rule name="WordPress Rule 3" stopProcessing="true">
                    <match url="^" ignoreCase="false" />
                    <conditions logicalGrouping="MatchAny">
                        <add input="{REQUEST_FILENAME}" matchType="IsFile" ignoreCase="false" />
                        <add input="{REQUEST_FILENAME}" matchType="IsDirectory" ignoreCase="false" />
                    </conditions>
                    <action type="None" />
                </rule>
                <rule name="WordPress Rule 4" stopProcessing="true">
                    <match url="^(wp-(content|admin|includes).*)" ignoreCase="false" />
                    <action type="Rewrite" url="{R:1}" />
                </rule>
                <rule name="WordPress Rule 5" stopProcessing="true">
                    <match url="^([_0-9a-zA-Z-]+/)?(.*\.php)$" ignoreCase="false" />
                    <action type="Rewrite" url="{R:2}" />
                </rule>
                <rule name="WordPress Rule 6" stopProcessing="true">
                    <match url="." ignoreCase="false" />
                    <action type="Rewrite" url="index.php" />
                </rule>
            </rules>
        </rewrite>
    </system.webServer>
</configuration>

All pages are redirecting to pnasb.net/wp-signup.php?new=pnasb.net

It’s not just admin pages, but all requests are pointing back here, so something must be configured a little wonky.

Both URLs in wp_options are set to http://pnasb.net

The only site in wp_site has a domain of pnasb.net, and its corresponding site url meta_value is http://pnasb.net

Any direction would be greatly appreciated.. I’ve tried lots of basic options for resolving this (setting the admin cookie path, clearing cookies, starting over from the beginning, etc)