@MrWilliamson Welcome to HP Community!
I understand that HP Envy x360 Sound moves to 100 after restart/waking up from sleep.
Do not worry. I will try to fix the issue.
I suggest you download and run the HP Support Assistant from this Link: https://www8.hp.com/us/en/campaigns/hpsupportassistant/hpsupport.html?jumpid=va_r602_us/en/any/psg/p...
HPSA will automatically search for all the latest drivers for your Notebook
- Click My devices in the top menu, and then click Updates in the My PC or My notebook pane.

- Click Check for updates and messages to scan for new updates.

- Review the list of updates. Updates with a yellow information icon are recommended. Updates with a blue information icon are optional.
- Click the update name for a description, version number, and file size.
- Select the box next to any updates you want to install, and then click Download and install.
Also ensure Windows is up to date
Select the Start button, and then go to Settings > Update & security > Windows Update , and select Check for updates. If Windows Update says your device is up to date, you have all the updates that are currently available
Please try creating a new user account on your computer.
Go to http://hp.care/2dWJKgW and follow the steps to create a new user account.
Keep us posted,
If you would like to thank us for our efforts to help you,
Give us a virtual high-five by clicking the 'Thumbs Up' icon below, followed by clicking on the "Accept as solution" on this post,
Have a great day!