When using slack with the "Flash taskbar for notifications" option turned on, the icon in the taskbar does not indeed flash when you receive a message.

Steps to reproduce:

1. Install Ripcord and link your slack account.
2. Ask someone to send you a message after having minimized the window.
3. Watch as nothing happens.

The interesting part is that this feature works with a Discord account, but not slack.

I'm running this on Windows 10 Pro, Version 10.0.17763 Build 17763.

Thanks for reporting. I've fixed this in the next version.