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Considering that your root filesystem is on /dev/sda7, I suspect that you’re running a multi-boot system, and that your /boot/efi/EFI/boot/bootx64.efi and /boot/efi/EFI/manjaro/grubx64.efi are out of sync.
I would recommend chrooting into your installed system from a USB stick with a recent Manjaro ISO, and then installing and running install-grub. It’s a shell script that will synchronize your UEFI stubs.
If the manjaro-chroot script on the live USB does not work — it should now, but if your ISO is not a recent one, then it’ll have difficulty with btrfs — then please use the method as laid out in the HowTo below. 