Journey Map is per default on the installation on the MyM Launcher. If you select to download it on the Update screen, you will get Error of duplicated mods. Could it be removed from the update list or from the default mod list?
Is this for the 1.10 server? because last I checked the 1.10 DW20 isn't on the MYM launcher yet (edit nvm I am wrong) Can you just deselect the mod from it as a temporary fix?
And for others reading this for an answer, delete the journey map that comes with the modpack as it's the older version. It should work then