Potential canonical issue with mapped domain

Hi all

I have a question in regards to the MU Domain Mapping plugin and a potential canonical issue. How come, all my sub-domains (the mapped ones) are flagged by the SEO Doctor browser plugin as:

” Page is not indexable because this page has a canonical URL set to [https://www.primary-domain.com/mapped-domain/] “

The primary domain is not being flagged with this issue, but all mapped domains are (the actual domain name of the mapped domain appears correct, but I am worried about the canonical alert). Is this something to be taken serious?

Thanks in advance for your help – MU Domain Mapping is a great plugin

https://www.ads-software.com/plugins/wordpress-mu-domain-mapping/