Tested the issue in Android and able to reproduce the issue. 

Steps Followed:
1. Launched the Chrome 
2. Navigated to galaxus.ch
3. Typed something in search bar
4. Tapped on switch tab button
5. Observed search popup is not visible

Chrome versions tested:
66.0.3338.0

OS:
Android 6.0.1

Android Devices:
Samsung S7

This seems to be a Non-Regression issue as same behaviour is seen since older builds

Please navigate to below link for log's and video--
go/chrome-androidlogs/808894

Thanks!

I suspect this is a site issue.  When you are in the tabswitcher, you are actually looking at a live version of the site.  The easiest way to see this is to play video content and enter the tab switcher and you'll see the content playing.

You can repro this on desktop as well.  Open this site in a new window and see that when you select a different window that the pop up hides until you click on it again.

You can see this on google's desktop site as well.

We are liking sending a blur to the site as it no longer has user focus, which I believe is the correct thing to do, so I think this is again something that is working as intended.

Adding mdjones@ in case this is something we want to investigate changing, but I suspect that would uncover the same amount of gremlins in the opposite direction.

Desktop Chrome:

Google.com in desktop mode - popup with search suggestions is hiding when you will switch from tab to another and return 

and 

this site - it doesn't happen (you still see search results after switching from tab to another and returning and you don't have to click).

Android Chrome:

Google.com in desktop mode - popup with search suggestions is NOT hiding when you will switch from tab to another and return (and you don't have to click on it)
 
and 

this site - it doesn't happen (you still see search results after switching from tab to another and returning and you don't have to click on it).

conclusion:

1. bug seems to be valid (preview seems not to show live site version) and I have strong reason to reopen it.

2. should I open another bug because of different google.com behavior between desktop and Android?

conclusion C.D:

3. I strongly believe now that we should see popup with search results in Android in tab preview for google.com too.

The most recently focused tab is always live in the tab switcher. From my testing, both google and the site in the description (in both mobile and desktop version) have the suggestions disappear when entering the tab switcher. My guess is that the input field loses focus, which is probably what the suggestions listen to.

Like tedchoc@ said, to test this on desktop:
 - Open two Chrome windows side-by-side with google results pages.
 - Try to have suggestions open on both at the same time.

Simply switching tabs in a single window would not demonstrate the issue because, on desktop, there is no tab switcher mode and you never see a preview of the tab you just left.

Since the behavior on mobile and desktop is identical in my testing, I'm marking this bug as WontFix.

Whether we want to send different events to the site when defocusing a tab is a separate issue.

Now I understand it, thank you