This is the most frustrating bug in Lenovo and Windows 10, where the external sound monitor is not detected after wakeup from sleep.
I have LG monitor with speakers connected via USB C to Lenovo X1 Extreme.

Took me a while to figure out where is the issue and there no enough clues about solving this problem.
Luckily, i found the solution after several attempt. I did few things here and still not sure which one is the solution.
Maybe you want to try it one by one.

1. Turn off Display into never
This is my highest suspicion about the bug. Go to Windows Power Options (click battery icon on right bottom).
Change the timeout where the turn of display set into “Never”. Once it’s done, test it with sleep and wake-up again

2. Uninstall Latest Quality update
If step 1 didn’t works, search for “Reset PC” in windows menu and choose advance for reboot reset.
Then, choose advance menu and choose uninstall latest quality update. See if this works.

3. Uninstall Drivers
If Step 1 and 2 not working, go to “Device management” and uninstall “Sound” and “Audio” Drivers.
Go to Control panel and uninstall “Nvidia audio”. Reboot and see the result.

Now, i don’t have any issue of missing external audio speaker after sleep in Windows 10 using Lenovo.