Installation on an external drive

I am trying to Install Ubuntu 18.0.4 on an external drive. I have done this many times, both on internal and external drives, and have never faced this issue before. So, I am reaching out to this community to get your suggestions.

I have an external portable drive in which I have installed Ubuntu, as I have had done in the past. However, when I try to boot from this external drive, it automatically directs me to the primary internal drive, which did not happen in the past with other external hard drives or USB drives.

I checked the Grub and it is installed; first partition flagged as Boot, ESP. I also see the Ubuntu drive mounted and listed in the Update-grub command.

This is what the grub shows:
Sourcing file /etc/default/grub' Sourcing file/etc/default/grub.d/init-select.cfg’
Generating grub configuration file …
Found linux image: /boot/vmlinuz-5.4.0-42-generic
Found initrd image: /boot/initrd.img-5.4.0-42-generic
Found linux image: /boot/vmlinuz-5.3.0-28-generic
Found initrd image: /boot/initrd.img-5.3.0-28-generic
Found Ubuntu 18.04.4 LTS (18.04) on /dev/sda3 -------> this is the external drive that is not booting
Adding boot menu entry for UEFI Firmware Settings

sda3 is the ubuntu that was installed on this external drive.
├─sda1 8:1 0 4.9G 0 part
├─sda2 8:2 0 16.1G 0 part
└─sda3 8:3 0 1T 0 part

Here are the grub files:
/media/sda1drive/EFI/BOOT# ls -alZ
total 4872
drwxr-xr-x 2 root root ? 4096 Aug 6 19:44 .
drwxr-xr-x 4 root root ? 4096 Aug 6 18:57 …
-rwxr-xr-x 1 root root ? 108 Aug 6 19:44 BOOTX64.CSV
-rwxr-xr-x 1 root root ? 1334816 Aug 6 23:07 BOOTX64.EFI
-rwxr-xr-x 1 root root ? 1213032 Aug 6 23:07 fbx64.efi
-rwxr-xr-x 1 root root ? 126 Aug 6 19:44 grub.cfg
-rwxr-xr-x 1 root root ? 1149312 Aug 6 19:44 grubx64.efi
-rwxr-xr-x 1 root root ? 1269496 Aug 6 23:07 mmx64.efi