Even if your site was switched to mobile-first indexing, it doesn't mean that Google will only crawl and render your pages using the GoogleBot mobile useragent. Google says they still send out the desktop GoogleBot to those pages to check on things.
In fact, JohnMueller from Google said there is like a 2-3:1 split between useragents. He said on Twitter "so when we shift to mobile first indexing for a domain, it's 2/3rd mobile, 1/3rd desktop."
He said it is totally normal to see a mix of useragents crawling your site. But when you are switched to mobile-first indexing, Google may crawl with both desktop and mobile useragents but will only show the indexed version, which is the mobile-first indexed version, not the desktop version.
Let me share all these tweets, so you see it in context:
No, but we still do some crawling with the "other" user-agent, so it would be normal to see a mix of desktop & mobile requests across a site.
— 🍌 John 🍌 (@JohnMu) September 4, 2019
Yes, we render pages with both desktop & mobile user-agents. Usually it's something like a 2-3:1 split, so when we shift to mobile first indexing for a domain, it's 2/3rd mobile, 1/3rd desktop (the numbers aren't fix, it's just what I commonly see)
— 🍌 John 🍌 (@JohnMu) September 4, 2019
If it has important content, structured data, images, or links in it, and it's not in the mobile version at all, then that would be missing when we shift the domain to mobile-first indexing.
— 🍌 John 🍌 (@JohnMu) September 4, 2019
I don't quite understand the question :), but I think you're asking if we index the content from the "non-primary" version -- that's not the case. If we switch to MFI, we only index the content from the mobile crawls.
— 🍌 John 🍌 (@JohnMu) September 4, 2019
We crawl both primarily to understand the relationship between desktop and mobile versions.
— 🍌 John 🍌 (@JohnMu) September 4, 2019
It's not something that needs to be "fixed," our crawling with both user-agents is by design (for example, we can't recognize the alternate desktop/mobile URLs without checking with a user-agent like that).
— 🍌 John 🍌 (@JohnMu) September 4, 2019
Forum discussion at Twitter.
