Domain Mapping plugin

Wp-admin is not accessible for several sites. I've read dozens and checklists and worked to apply solutions I've found with no success. May need to pay someone on your side or other wise to log in and see what you can determine. Checked the associated WP files, etc.
Site is working correct and sites are using the mappings correctly, just showing "invalid" status on the mapping page for three or four sites. This was working for a year or so and recently broke for some reason. Just the log in to WP admin and the invalid notice. Don't believe we've added any new plugins, and I've tried disabling a few to see if that would help. Working on this for several days now. Thanks!