Domain Mapping plugin is causing login redirect loop but if removed, cannot access sub sites

I have the old WPMUDEV domain mapping plugin installed on I have transitioned most sites over to native mapping so it is not being used much anymore. The issue is that it seems to be causing login redirect loops for the network admin access.

If I disable the plugin via FTP, I’m able to login to the network but then I cannot log into any subsite, seeing the following “ERROR: Cookies are blocked or not supported by your browser. You must enable cookies to use WordPress.” (note again, the front end stays up and running for these sites as the domains are mapped natively now. )

When I reactive the plugin, I can once again access the subsites without issue but I can no longer access the network admin (redirect loop to the login page comes back).

Is there a process to disable the domain mapping plugin? Are there additional settings or code in wp-config or other files that I must manually modify to avoid the Cookie error?

I have another installation on the same server ( that never had the domain mapping plugin and it continues to work great.

Please advise.