Hi @SamTheCanadian! What error is received when attempting to remove the failed sensor? Check out our help center article for steps on how to remove this device in the Ring app, just to ensure all the right steps are being followed.
As it sounds like you are following these steps, there is another way to remove device through Base Station options in the Ring app. Similar to the steps in the help center article above, visit the Alarm Base Station page in your Ring app. Next, select the settings cog (top right) on the Base Station page, then select Advanced Options. Here you will see a protocol adapters section with Zwave as an option. Upon tapping Zwave, you will see the option for Remove device, which should allow you to remove the failed device. I hope this helps!