Fedora 31 kernel 5.5.10 cannot restart but power off + power on works fine

Using Fedora 31 with kernel 5.5.10 on a Lenovo Thinkpad T480 with the latest firmware.
When restarting (ctrl+alt+canc, or “reboot” from terminal), the pc hangs at Lenovo red startup logo, with fan running high, and becomes totally unresponsive.
If powering off from Gnome (and even after forcing power down when unresponsive), the boot sequence is normal, and Fedora starts just fine.
Any suggestions would be appreciated.

What about older (or newer) kernels, do they work fine?

Yes, they work fine. However, also with kernel 5.5.8 it is not possible to restart.

I’ve encountered bugs like this before with some hardware on other distros. There it was something to do with the kernel’s acpi detection.

Have you tried adding the “acpi=force” option in GRUB? That’s worked for me before.
If not you can try “acpi=off” instead, but that will kill your power management.

I tried adding the options to GRUB but with no results.

I then reinstalled Fedora 31 from scratch; same issues also with older kernel. I noted that the hanging and high fan on reboot was present even when rebooting from bios. So downgraded firmware from v1.31 to v 1.29: same issues. I then re-installed firmware 1.31, and now rebooting is possible, as well as wake-up from lid open.

However, on every start-up, a message appears stating “The connected AC adapter has a lower wattage than the recommended AC adapter which was shipped wit the system. To use AC power, please connect the AC adapter which was shipped with the system. Press the ESC key to continue”. The adapter is the one shipped with the pc. Anyway, pressing ESC allow the boot (or reboot) to continue, the adapter is charging the battery properly, and everything ACPI (keyboard illumination, plugging-unplugging the adpater, etc.) is working fine.

Hopefully a new firmware update from Lenovo will resolve this issue (I have read T480 had problems with the thunderbolt USB-C controller, maybe is this).