Possible reasons I’m thinking about:
- Google quality/algorithm update
there was indeed a recent update, so that could be a reason:
https://www.blackhatworld.com/seo/google-may-2026-core-update-what-are-your-thoughts.1818437/
Thin or low-value content
also possible, but highly unlike for mass de-indexation
possible, but from what you described it looks like you already checked the technical part (robots.txt, noindex tags, etc...), so I don't think that this is it
Canonical/indexing conflict
canonical is not reason for de-indexation, not for 300 pages at once anyway. So, this is not the reason IMO
AI content or over-optimization signals
AI content can be a reason, over-optimization not. But I don't think it's any of these anyway....
crawl budget is a thing, and it's important for fresh sites more than for established ones that google trusts. But crawling issues don't lead to mass de-indexation, if your crawl budget is low google will not index those URLs simply because it doesn't find them because it doesn't have enough crawl budget to crawl them, but it doesn't de-index them so there must be another reason...
What should I audit first, and is recovery possible without changing the domain?
sure it's possible. The fact that your site can still be found in google tells me that the issue is elsewhere.
Based on the info you've provided, my guess is that it's one of the following reasons:
- your site is fresh, therefore google doesn't trust it yet, therefore you need to work on building up its trust and authority and then - at some point - your pages will get back into index.
- content quality. AI or not, if your content doesn't address the intent it can get de-indexed. This being said, I still don't think that the content is the issue, because we're talking about mass de-indexation, not about a few pages that google doesn't like. So, while content can lead to de-indexation, I genuinely don't think this is the reason, but I've mentioned it just in case that all other reasons fail
- internal links (can also lead to de-indexation, but - again - I find it highly suspicious to lead to MASS de-indexation, so something else is at fault)
- you're using an expired domain that carries some penalty with it and which could be hard to clean, which is why - until cleaning happens - google refuses to index it (this is actually one of the hunches that I have for what could be wrong with your site)
- you're operating in a ultra tough, or ultra highly regulated niche (governmental stuff, CBD oil / peptides / viagra stuff, movie streaming / content piracy stuff, etc) that google don't like and / or which they regulate heavily, in which case you will need a lot of trust and EEAT bullshit to impress google in order for them to even index you. Either this, or it's a copyright infringement / DMCA type of thing...
If I were to put my money on it, I would say that - of all of these reasons (and considering that we are talking about mass de-indexation, not just single pages) - I would say it's either:
- expired domain that carries penalty
- tough / heavily regulated or restricted niches, and / or mass DMCA-related stuff
- fresh site with no / low trust and authority
- current google update
So, I would look into these things first...
Would appreciate genuine expert suggestions.
My suggestions were genuine, but I'm not an expert, but since you bumped the thread and no one replied... I thought I'd give a helping hand, so take it or leave it, I don't care and I don't mind
