Try the following:
When the headphones and smartphone are connected, a Google Assistant notification may pop up. If you tap the notification, the assignment of the headphone button or the touch sensor function will be switched to Google Assistant.
If this happens, change the assignment back to Ambient Sound Control by using Headphones Connect.
If the same notification appears again the next time you connect, do not tap the notification, but swipe the notification to turn it off.
If a function other than Ambient Sound Control, such as Google Assistant, is assigned to the button or touch sensor, you cannot switch the Noise Canceling function or Ambient Sound Control function by using the headphone’s button or touch sensor.