Issue resolved.
Was permission 0755 on Mdocs folder. changed it to 777 and now uploads as before without error.
May be of use to someone else.
Also seeing permission errors, but nothing has changed unless its an OS update that has now imposed permissioning that was there before
file_put_contents(/datadrive/atlasorg/public_html/wp-content/uploads/mdocs/mdocs-files.bak): failed to open stream: Permission denied in /datadrive/atlasorg/public_html/wp-content/plugins/memphis-documents-library/includes/mdocs-settings.php on line 48: /usr/local/cpanel/cgi-sys/ea-php72
Sorry, should have put this info.
PHP 7.2
WP: 5.4.2–en_GB
M-Docs: 3.10.10
Thanks
Andrew