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Killer tool. Till now for me, Cora is the best. But you have to know how to use properly.

Last night they updated their system.

Domain Authority > Domain Authority 2.0

• https://moz.com/domain-authority-2.0
• https://moz-static.s3.amazonaws.com/products/landing-pages/announcements/Authority_Scoring_Guide.pdf
• https://moz.com/community/q/a-new-and-improved-domain-authority-is-on-the-way

Follow these two post

https://moz.com/blog/comprehensive-analysis-domain-authority

https://moz.com/blog/domain-authority-seo

If they are relevant then you can get some value.

As far as I know when something makes new update they change lots of things. That's not only you but many other people facing this same problem. But creating good content, fix on page and internal linking for a good result.

As long as the subdomain is on a good host, has good UX/content and links well w/the parent. It also requires more maintenance than the parent. But if you can maintain everything then it's ok.

Google will sometimes use the description tag from a page to generate a search results snippet if we think it gives users a more accurate description than would be possible purely from the on-page content." (Bold is mine) https://support.google.com/webmasters/answer/35624?hl=en

GMB and citation are working. But before everything complete your homepage SEO.

You can go for it.

Your friend can start with ahrefs SEO for a beginner then can watch this one. Just found this playlist is better than some other so-called experts video on basic SEO.   https://youtu.be/dpwqh-dCfkI?list=PLNR9ExBpEoWztu0wD2SBTMcm9Y_s4llH0

I don't think so, that it will create a problem.

Did you check  your robot txt file? Or check if any plugin creating this problem.

Lots of people facing this same problem. It happening because Google has some technical issues.

Don't worry, it is happening because of Google technical issues. They are trying to fix there a problem

I prefer not to allow search result pages to be indexed.

This is happening because Google having some technical problem Don't worry it will be fixed soon.