Can you try running it on the terminal and see if any errors are reported?

I assume you mean running plasma-discover from the terminal? I don't know how to use fwupdmgr directly actually, so I went via plasma-discover. In the Discover window, I "installed" the update for the Intel Management Engine. This is all the output I got:

$ plasma-discover
adding empty sources model QStandardItemModel(0x5643b71d21f0)
file:///usr/lib/x86_64-linux-gnu/qt5/qml/org/kde/kirigami.2/private/PrivateActionToolButton.qml:76:5: QML Binding: Binding loop detected for property "value"
no component found for "org.kde.neon.neon"
file:///usr/lib/x86_64-linux-gnu/qt5/qml/org/kde/kirigami.2/ScrollablePage.qml:203:9: QML MouseArea: Binding loop detected for property "implicitHeight"
file:///usr/lib/x86_64-linux-gnu/qt5/qml/org/kde/kirigami.2/ScrollablePage.qml:203:9: QML MouseArea: Binding loop detected for property "implicitHeight"
Hspell: can't open /usr/share/hspell/hebrew.wgz.sizes.
kf.sonnet.clients.hspell: HSpellDict::HSpellDict: Init failed
qrc:/qml/DiscoverPage.qml:17:13: QML InlineMessage: Cannot anchor to an item that isn't a parent or sibling.

Can you try installing it manually using the `fwupdmgr` command?

First run `fwupdmgr get-upgrades`

Then run `fwupdmgr install` and choose the number for the device that has an update available.

Thanks for helping! I did `fwupdmgr get-upgrades`, and weirdly, it reported immediately that it also installed the upgrades (instead of just downloading them). Also, it doesn't tell me device numbers so I don't know how to continue with the other part of your advice. I restarted my system, and Discover still indicates that it wants to update the Lenovo Intel Management Engine.

```
$ fwupdmgr get-upgrades
Devices with no available firmware updates:
 • Bolt Receiver
 • LIFT
 • Radio
 • UEFI Device Firmware
Devices with the latest available firmware version:
 • Embedded Controller
 • Intel Management Engine
 • MZVLB1T0HALR-000L7
 • System Firmware
 • Thunderbolt host controller
________________________________________________

Devices that have been updated successfully:

 • UEFI Device Firmware (0.1.11 → 0.1.13)
 • UEFI Device Firmware (0.1.13 → 0.1.14)
 • System Firmware (0.1.39 → 0.1.40)
 • Intel Management Engine (192.72.1757 → 192.81.1753)
 • System Firmware (0.1.38 → 0.1.39)

Uploading firmware reports helps hardware vendors to quickly identify failing and successful updates on real devices.
Upload report now? (Requires internet connection) [Y|n]:
n

Do you want to disable this feature for future updates? [y|N]:
n
Declined upload
```

Thanks. So after rebooting, `fwupdmgr get-upgrades` shows no available firmware updates, but Discover doesn't agree?

Huh, it's weird. I did it yesterday a few times, and I always go the output that I shared in my last comment. But now I did it again, and the output now indicates that there was indeed a problem. I guess a fwupd bug. I can report it on their github.

$ fwupdmgr get-upgrades
________________________________________________

Devices that were not updated correctly:

 • Intel Management Engine (192.81.1753 → 192.90.2072)

Yep, so Discover is just showing you that.

I guess we can do a better job of indicating that there was an error state that isn't Discover's fault, though.

I ran into the same problems, with the same firmware update. 

Discover continues to report an update available. But `fwupdmgr get-upgrades` shows:

```
Devices with no available firmware updates: 
 • ELAN0686:00 04F3:320D
 • Fingerprint Sensor
 • Integrated Camera
 • Intel Management Engine
 • UEFI Device Firmware
 • UEFI Device Firmware
 • UEFI Device Firmware
 • UEFI Device Firmware
 • UEFI Device Firmware
 • UEFI Device Firmware
 • UEFI Device Firmware
 • UEFI Device Firmware
 • UEFI Device Firmware
 • UEFI Device Firmware
Devices with the latest available firmware version:
 • Embedded Controller
 • KBG5AZNV1T02 LA KIOXIA
 • System Firmware
────────────────────────────────────────────────
Devices that were not updated correctly:
 • Intel Management Engine (1.27.2176 → 257.27.2176)
Uploading firmware reports helps hardware vendors to quickly identify failing and successful updates on real devices.
Upload report now? (Requires internet connection) [Y|n]: y
```

I proceeded to upload the report as requested by the tool (to hopefully help draw attention to the bug). 

An interesting note, on reboot, the firmware update tool does kick in - but the progress bar remains at 0% till after a certain time, Fedora just boots. Is there something I can do at that stage to find more logs?

I'm closing this as it is a fwupdmgr bug, as discussed.