To clarify: After step 5:

Step 6: Click the notification as it appears in the upper right corner of the OS.

Tried testing the issue on reported chrome version #70.0.3538.110 using Mac 10.14.1 by following below steps.

Steps:
=====
1.Launched chrome normally.
2.Launched second instance of chrome through the terminal(using command mentioned in comment#0).
3.Signed into the Slack account and allowed notifications.
4.Moved the focus to another tab.
5.When a new message is received, a notification has been received.
6.Clicked on notification, it navigated to the correct window+tab.
7.Tried testing same, by moving focus to the prior window opened.
8.When a new message is received unable to see any notification.

Attached screencast for reference.
@reporter: Could you please review attached screencast and let us know if anything is being missed here.
Thanks.!

Deleted: 909646.mp4 4.7 MB

	909646.mp4 4.7 MB View Download

That is unfortunately incorrect. Since you did not change "/some/path" to something valid, you do not get a NEW chrome instance, you just get the same chrome instance you already had only in a second window of that instance.

Please change "/some/path" to (on mac): "/Users/<MY USERNAME>/<SOME DIR YOU CREATED SO YOU DONT POLLUTE YOUR HOME DIR>"

In my case it is e.g. mkdir -p "/Users/myuser/secondchrome"

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

For more details visit https://www.chromium.org/issue-tracking/autotriage - Your friendly Sheriffbot

Tried testing issue on reported chrome version #70.0.3538.110 using Mac OS 10.14.1 by following below steps.

Steps:
=====
1.Launched chrome normally.
2.Made a directory using mkdir -p "/Downloads/myuser/secondChrome"
3.In terminal using "/Applications/Google\ Chrome.app/Contents/MacOS/Google\ Chrome --user-data-dir=/Downloads/myuser/secondChrome > /dev/null 2>&1 &" launched second instance of chrome.
4.Signed into Slack account and allowed notifications.
5.Moved focus to another tab, and received a new message notification.
6.After clicking on the notification, it switched to the tab where my slack account has been opened without opening a new tab.
7.Tested the same by moving focus to prior opened window and found the same result as mentioned in Step6.

Attached screencast for reference.
@reporter: Could you please review attached screencast and let us know if anything is being missed here. Request you to provide the screencast of the issue so that it would be really helpful in triaging the issue.
Thanks.!

Deleted: 909646_New.mp4 3.3 MB

	909646_New.mp4 3.3 MB View Download

I can see clearly in your video that Chrome says "Google Chrome cannot read and write to its data directory: /Downloads/myuser/secondChrome", which is a clear indication that you did not get a completely new instance of Chrome, just a new window in the same Chrome instance.

In step 3 you clearly point Chrome to ANOTHER directory than the one you created!
My guess is that you created the directory "Downloads/myuser/secondChrome" inside "/Users/<myuser>" ===> The actual created directory is "/Users/<myuser>/Downloads/myuser/secondChrome" - But then you launch chrome using "/Downloads/myuser/secondChrome" which obviously is a directory that does NOT exist.

May I suggest that you do "pwd" in the terminal after creating your chrome profile directory so that you can make sure that the directory you created actually exists.

Please make sure, very carefully, that the directory you created and the path that you give to the new chrome instance are EXACTLY THE SAME, and that it does in fact exist!

Thank you!

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

For more details visit https://www.chromium.org/issue-tracking/autotriage - Your friendly Sheriffbot

Running two instances of Chrome with different user-data-dirs is generally an unsupported scenario. We recommend that you use separate profiles (see the profile selector next to the 3-dot button on the top of Chrome).

In your case, I suspect Slack has also registered for notifications in your first instance of Chrome. You'll need to clear that permission in your first instance to avoid duplicate notifications as well as activating the correct instance of Chrome in the unsupported scenario.

Well seeing as this has worked perfectly up until recently I am disappointed, but we all have a job to do I guess.