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Hi, My first time posting here, I am just looking for some feedback on a indexation issue we have with a client and any feedback on possible next steps or items I may have overlooked. To give some background, our client operates a website for the core band and a also a number of microsites based on specific business units, so you have corewebsite.com along with bu1.corewebsite.com, bu2.corewebsite.com. The content structure isn't ideal, as each microsite follows a structure of bu1.corewebsite.com/bu1/home.aspx, bu2.corewebsite.com/bu2/home.aspx and so on. In addition to this each microsite has duplicate folders from the other microsites so bu1.corewebsite.com has indexable folders bu1.corewebsite.com/bu1/home.aspx but also bu1.corewebsite.com/bu2/home.aspx the same with bu2.corewebsite.com has bu2.corewebsite.com/bu2/home.aspx but also bu2.corewebsite.com/bu1/home.aspx. Therre are 5 different business units so you have this duplicate content scenario for all microsites. This situation is being addressed in the medium term development roadmap and will be rectified in the next iteration of the site but that is still a ways out. The issue
About 6 weeks ago we noticed a drop off in search rankings for two of our microsites (bu1.corewebsite.com and bu2.corewebsite.com) over a period of 2-3 weeks pretty much all our terms dropped out of the rankings and search visibility dropped to essentially 0. I can see that pages from the websites are still indexed but oddly it is the duplicate content pages so (bu1.corewebsite.com/bu3/home.aspx or (bu1.corewebsite.com/bu4/home.aspx is still indexed, similiarly on the bu2.corewebsite microsite bu2.corewebsite.com/bu3/home.aspx and bu4.corewebsite.com/bu3/home.aspx are indexed but no pages from the BU1 or BU2 content directories seem to be indexed under their own microsites. Logging into webmaster tools I can see there is a "Google couldn't crawl your site because we were unable to access your site's robots.txt file." This was a bit odd as there was no robots.txt in the root directory but I got some weird results when I checked the BU1/BU2 microsites in technicalseo.com robots text tool. Also due to the fact that there is a redirect from bu1.corewebsite.com/ to bu1.corewebsite.com/bu4.aspx I thought maybe there could be something there so consequently we removed the redirect and added a basic robots to the root directory for both microsites. After this we saw a small pickup in site visibility, a few terms pop into our Moz campaign rankings but drop out again pretty quickly. Also the error message in GSC persisted. Steps taken so far after that In Google Search Console, I confirmed there are no manual actions against the microsites. Confirmed there is no instances of noindex on any of the pages for BU1/BU2 A number of the main links from the root domain to microsite BU1/BU2 have a rel="noopener noreferrer" attribute but we looked into this and found it has no impact on indexation Looking into this issue we saw some people had similar  issues when using Cloudflare but our client doesn't use this service Using a response redirect header tool checker, we noticed a timeout when trying to mimic googlebot accessing the site Following on from point 5 we got a hold of a week of server logs from the client and I can see Googlebot successfully pinging the site and not getting 500 response codes from the server...but couldn't see any instance of it trying to index microsite BU1/BU2 content So it seems to me that the issue could be something server side but I'm at a bit of a loss of next steps to take. Any advice at all is much appreciated!