So, I recently reinstalled Windows 10 and then went to install Manjaro on top of that. During the install of Manjaro, I set the 100MB FAT32 partition to mount at /boot/efi/ and to carry the boot and efi flags (without formatting it).
I also created an ext4 partition to mount at '/' and a swap partition, and completed the Manjaro install.
After rebooting, the computer boots directly into Windows 10, not Manjaro. I tried repeating the process a second time and got the same result. I can't think of what could possibly cause this?