MultiBeast 10 can't mount or unmount EFI partition on High Sierra volume

[davidr418]

After finally getting the apfs.efi details figured out, I finally have a working, bootable APFS volume with High Sierra. Yay!

But all's not well just yet. I have no sound, and some USB ports don't work, so I want to use MultiBeast 10.0 to install the proper audio driver and expand the number of USB ports available on my ASUS Z270-i STRIX motherboard.

Hm. When I click "Build" and select my volume, MultiBeast fails instantly. The log says:

11/11/17 19:35:05 - Starting MultiBeast 10.0.0-20171106
11/11/17 19:35:28 - Mounting EFI
11/11/17 19:35:28 - Mounting EFI failed. Exiting.

Weird. But I can mount the EFI partition with Clover Configurator or EFI Mounter, so I do that and try again. This time MultiBeast works for several minutes, then fails again. Now the log shows:

11/11/17 19:38:25 - Mounting EFI
11/11/17 19:38:25 - Installing 'Drivers > Audio > Realtek ALCxxx > ALC1220A (ASUS ROG STRIX Only)'
11/11/17 19:39:02 - Installing 'Drivers > USB > Increase Max Port Limit 200 Series'
11/11/17 19:39:47 - Unmounting EFI
11/11/17 19:39:48 - Unmountaing EFI failed. Exiting.

OK. So MultiBeast can't mount, or unmount, the EFI partition, and its failure to do so means I'm stuck with no sound and limited USB ports. I've searched the forums here, and the only applicable thread I can find is this, and redoing the entire install using Legacy Boot Mode seems a bit overkill, really.

 

[davidr418]

I see there's a new MultiBeast, 10.1. Let's give that a try.

Nope. Still fails mounting the EFI partition. Here's what the log file says:

11/12/17 12:58:56 - Starting MultiBeast 10.1.0-20171111
11/12/17 12:59:19 - Mounting EFI
11/12/17 12:59:19 - EFI partition for volume does not contain a CLover config.plist. Exiting.

Sounds reasonable, except that there is a config.plist on the EFI partition, right there inside the Clover folder where you'd expect it to be...