Steps to reproduce:

Load the following markup in Chrome and append "Message 2" to the div's innerText with JavaScript:

<div aria-live="polite" aria-atomic="false">
   Message 1
</div>

Actual behavior:

NVDA announces "Message 1 Message 2". (all the content in the aria-live region)

Expected behavior:

NVDA announces only "Message 2". (the changed content in the aria-live region)

System configuration

NVDA installed/portable/running from source:

Installed

NVDA version:

2019.3.1

Windows version:

Windows 10 Version 1909 Build 18363.657

Name and version of other software in use when reproducing the issue:

Chrome Version 80.0.3987.132 (Official Build) (64-bit)

Other information about your system:

Other questions

Does the issue still occur after restarting your computer?

Yes

Have you tried any other versions of NVDA? If so, please report their behaviors.

Yes, Portable NVDA 2019.2. Same behavior

If addons are disabled, is your problem still occuring?

Yes

Did you try to run the COM registry fixing tool in NVDA menu / tools?

Yes