Yoast – WordPress sub directory install redirect issue

Wordpres 4.6.1

WordPress installed in Root HTML folder on the server. /public_html/

WordPress Development site installed in sub directory /public_html/_DEV/

After installing YOAST SEO Via Plugin Add New to /public_html/_DEV/

I cannot access the wp-admin and it keeps redirecting to the root website URL /public_html/

I removed Yoast from the plugin’s directory /public_html/_DEV/wp-content/plugins/wordpress-seo/ to /public_html/_DEV/wp-content/plugins/_BAK/wordpress-seo/ so it can no longer be read as a plugin

Then I can magically access /public_html/_DEV/wp-admin

It Appears that YOAST is applying a redirect to the subdirectory install /public_html/_DEV/wp-admin/ to the root WordPress install url /public_html/index.php

Your assistance is urgently required.

I can supply login details to the development site, and FTP access.