Hi Dries! I am very sorry to hear about the issues you are experiencing with the volume control on your Samsung Soundbar. If possible, you may want to try updating the Firmware of the soundbar to the latest version (ver.1010.1). You can update the soundbar via the SmartThings app, or by using a USB device. Should this not resolve the issue, please try re-initializing the soundbar by pressing the + and - buttons on top of the soundbar for 5 seconds, or until "INIT" appears on the display. Please know, re-initializing the soundbar will reset the settings on the soundbar. Any audio adjustments will need to be re performed on the soundbar to tune the audio to your preference. If you continue to experience issues, please reach out to Samsung Support at: 1-800-SAMSUNG (ask for Soundbars), available 8AM - 12AM EST, 7 days a week, or Chat with us on Samsung.com: https://www.samsung.com/us/support/contact/
^Tim