Thanks for filing the issue!

Tried checking the issue on reported chrome version 66.0.3359.139 using Windows 10 with the below mentioned steps.
1. Launched Chrome
2. Navigated to https://www.google.com/url?q=https%3A%2F%2Fweb-push-book.gauntface.com%2Fdemos%2Fnotification-examples%2F&sa=D&sntz=1&usg=AFQjCNHPhK5vU4SxhHEFKNjWWx5y9wAKcA
3. Clicked on Allow-> Clicked on buttons to get the notifications.
We were able to get only three notifications on screen, in both reported 66.0.3359.139 and M65(65.0.3325.181) versions.

@Reporter: As this issue seems to be very similar to that of  Issue 845140  and  Issue 837119 , Please confirm on it. And providing us with any sample test URL/file which shows around 10 notifications would help us, as we are not very sure about the usage of URL provide above is apt for testing this. Any further inputs may be helpful.

Thanks!

Tested this url https://web-push-book.gauntface.com/demos/notification-examples/ with button Title & Body in section Desktop & Mobile
Linux chromium 66 show all pushes
Windows xp chrome 49 show 3 pushes, after close show next 3 pushes
Windows 7 chrome 66 show 3 pushes, next pushes not show
Not sure about chrome 65, but I'm sure old chrome worked good with pushes, maybe need check ver 64 or older

Thank you for providing more feedback. Adding the requester to the cc list.

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Thank you for reporting the issue! This is a duplicate of  Issue 837119 , which has already been resolved.