Ubuntu Lenovo Server takes 3 hours to reboot

Since the beginning of the month, automatic reboot after kernel change takes … 3 hours.

It is a Lenovo Thinksystem server in a datacenter.

journalctl -b -1 ends with:

juil. 23 03:02:25 host systemd-shutdown[1]: Sending SIGTERM to remaining processes...
juil. 23 03:02:25 host systemd-journald[658]: Journal stopped

and journalctl -b starts with:

juil. 23 06:16:26 host kernel: microcode: microcode updated early to revision 0x2006906, date = 2020-04-24
juil. 23 06:16:26 host kernel: Linux version 4.15.0-112-generic (buildd@lcy01-amd64-027) (gcc version 7.5.0 (Ubuntu 7.5.0-3ubuntu1~18.04)) #113-Ubuntu SMP Thu Jul 9 23:41:39 UTC 2020 (U
juil. 23 06:16:26 host kernel: Command line: BOOT_IMAGE=/boot/vmlinuz-4.15.0-112-generic root=UUID=7b9c74b1-d80e-457e-957a-32be0fca891e ro

I have a GRUB_TIMEOUT=0 so I have no idea of what could be the issue.

Edit:

One weird thing is that lshw used to show the server model:

product: ThinkSystem SR590 -[7X99CTO1WW]- (7X99CTO1WW)
vendor: Lenovo
version: 04

And now:

    description: Rack Mount Chassis
    product: -[none]- (none)
    vendor: Lenovo
    version: none
    serial: none
    width: 64 bits
    capabilities: smbios-3.2 dmi-3.2 smp vsyscall32
    configuration: boot=normal chassis=rackmount family=ThinkSystem sku=none
  *-core
       description: Motherboard
       product: -[none]-
       vendor: Lenovo
       physical id: 0
       version: none
       serial: none
       slot: none
     *-firmware
          description: BIOS
          vendor: Lenovo
          physical id: 0
          version: -[TEE128O-1.51]-
          date: 10/30/2018
          size: 64KiB
          capacity: 15MiB
          capabilities: pci pnp upgrade shadowing cdboot bootselect edd int14serial acpi usb biosbootspecification uefi
     *-cpu:0
          description: CPU
          product: Intel(R) Xeon(R) Silver 4110 CPU @ 2.10GHz

Edit 2:

It seems to be stuck on that screen for hours: