Ubuntu 18.04 “grub-install: error: cannot find EFI directory”

I have this issue on multiple ubuntu 18.04 servers.

During a regular apt update && apt upgrade I get this error:

Setting up grub-efi-amd64-signed (1.167~18.04.1+2.04-1ubuntu44) ...
Installing for x86_64-efi platform.
grub-install: error: cannot find EFI directory.
dpkg: error processing package grub-efi-amd64-signed (--configure):
installed grub-efi-amd64-signed package post-installation script subprocess returned error exit status 1

I'm on a server, I don't use grub and I never heard of EFI, I didn't change any of its settings as far as I know.

I have /dev/md1 mounted on /boot, and I see I have a directory /boot/efi but it's empty.

How can I fix this issue?

fdisk -l:

Disk /dev/sda: 1.8 TiB, 2000398934016 bytes, 3907029168 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: gpt
Disk identifier: F4BBD515-6E5E-4152-AD41-6D80A4A69583

Device          Start        End    Sectors    Size Type
/dev/sda1          40       2048       2009 1004.5K BIOS boot
/dev/sda2        4096 3905976319 3905972224    1.8T Linux RAID
/dev/sda3  3905976320 3907022847    1046528    511M Linux swap


Disk /dev/sdb: 1.8 TiB, 2000398934016 bytes, 3907029168 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: gpt
Disk identifier: 2C2D425C-9EAF-472D-8820-068D587A47D0

Device          Start        End    Sectors    Size Type
/dev/sdb1          40       2048       2009 1004.5K BIOS boot
/dev/sdb2        4096 3905976319 3905972224    1.8T Linux RAID
/dev/sdb3  3905976320 3907022847    1046528    511M Linux swap


Disk /dev/md2: 1.8 TiB, 1999857713152 bytes, 3905972096 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes

fdisk -l, second server:

Disk /dev/sda: 223.6 GiB, 240057409536 bytes, 468862128 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0x762b7381

Device     Boot     Start       End   Sectors   Size Id Type
/dev/sda1  *         4096   1050623   1046528   511M fd Linux raid autodetect
/dev/sda2         1050624 467808255 466757632 222.6G fd Linux raid autodetect
/dev/sda3       467808256 468854783   1046528   511M 82 Linux swap / Solaris


Disk /dev/md2: 445.1 GiB, 477958766592 bytes, 933513216 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 524288 bytes / 1048576 bytes


Disk /dev/md1: 511 MiB, 535756800 bytes, 1046400 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes


Disk /dev/sdb: 223.6 GiB, 240057409536 bytes, 468862128 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0x41167758

Device     Boot     Start       End   Sectors   Size Id Type
/dev/sdb1  *         4096   1050623   1046528   511M fd Linux raid autodetect
/dev/sdb2         1050624 467808255 466757632 222.6G fd Linux raid autodetect
/dev/sdb3       467808256 468854783   1046528   511M 82 Linux swap / Solaris