question

I would like to see if the issue can be resolved by removing some extra data that remains even after a standard Windows uninstall.

Some images of the process can be found in the comments by Kim on her post for resolving softphone crashes, but I'll include a more detailed process for uninstalling and removing the extra data on Windows or Mac:

Windows

1. Open RingCentral for Windows
2. Press the Ctrl and F1 keys
3. Select "App data folder" in the context menu that appears, a new explorer window will open.
4. If you are unable to open the RingCentral for Windows app or this process does not work for you, then find these files in Windows File Explorer by navigating through this path on your computer: C:\Users[username]\AppData\Local\RingCentral\SoftPhone
5. Log out of RingCentral for Windows before continuing, and close the application. Also close the application background process by clicking on the ^ icon in the taskbar at the bottom right of your screen, then right-click the RingCentral icon and select 'exit' (see link above for images).
6. In the explorer window that is still open, you should see the contents of the RingCentral folder, highlight all of these items and delete them. If you see a message that the Logs are still in use you may skip deleting this item.
7. Uninstall RingCentral using the uninstall utility in Windows
8. Download the latest version of RingCentral for Desktop by logging into service.ringcentral.com and going to Tools > Desktop Apps in the top menu
9. Install, open, and log into RingCentral for Windows.

macOS

1. Open RingCentral for Mac
2. Press the Command () and F1 keys
3. Select "App data folder" in the context menu that appears, a new Finder window will open.
4. If you are unable to open the RingCentral for Mac app or this process does not work for you, then find these files in Finder by navigating through this path on your computer: ~/Library/Application Support/RingCentral (~ is the directory of the current user, Apple has instructions to get to the user library)
5. Log out of RingCentral for Mac before continuing, and quit the application by going to File > Quit RingCentral for Mac.
6. In the Finder window that is still open, you should see the contents of the RingCentral folder, highlight all of these items and delete them. If you see a message that the Logs are still in use you may skip deleting this item.
7. Delete teh RingCentral app by dragging the icon from the Applications folder to the trash
8. Download the latest version of RingCentral for Desktop by logging into service.ringcentral.com, ensure you are in a user extension and not admin view, and going to Tools > Desktop Apps in the top menu
9. Install, open, and log into RingCentral for Mac.