Developing a mod takes time and the amount of hours needed to catch up to certain patches depends on how much has been changed between patches. Large updates like 1.12 over 1.11 means development of the mod is stretched out to fix new issues, remove old mechanics and use the new replacement mechanics, and lastly to update the provinces that change (new ones or updated histories).

So while the mod is behind, you can always revert EUIV to an older version.

This is how it is done:

In your Steam Library find Europa Univeralis IV.
Right Click Europa Univeralis IV and select Properties, this will open up the Properties for Europe Univeralis IV.
Go to the Betas Tab.
Select from the list of available "betas" the most recent version of the game that will work for the mod (Currently 1.11.4).
Hit Apply, Steam will update Europa Univeralis IV to the old files. When completed the game can be played.
Start Europa Univeralis IV, the mods that are for that version of the game will be available to play.
Select the mod you want play and start the game, it will load.

That's all that is really to it.

To revert the game to its current version, just repeat the instructions above and select NONE.