Hangouts app will soon stop working on desktops and laptops. I don't know what happens if the Hangouts app and extension are used at the same time, but we have been forewarned not to do so.
"The support document doesn't go into too much detail about the schedule to expect in the warning which now appears, only stating that it "will stop working soon." In this transition, Hangouts users are warned not to use both the app and the extension simultaneously."
Evidently many people have both the Hangouts app, which pops up on their screens as a bubble picture when on a call with others, etc., and the Hangouts extension on their Chrome Browsers, and for the past four years or so they could both be used without interfering with one another. But Google will soon be doing away with the Hangouts app for Chrome, and if people leave it installed and also have the Hangouts extension installed, apparently calling functions may adversely affected if used at the same time or simultaneously. Perhaps at the same time just means having them both installed at the same time. If you use a pc, you can find your apps listed below you extensions via the tools>extension window.