Yes, but only the first time after an update to the vanilla game, an update to any mod you're currently running, or if you changed the mods you're running. Most people report it taking anywhere from 10-40 minutes to completely content build EF with all packs on first install depending on your computer. This is NORMAL and future loading times for the game should be much, much shorter. Be patient. Go get some coffee or something. Take a walk. A watched progress bar never finishes.

If it's taking more than 40 minutes to build please compare your system specs with Staxel's requirements. if you're really close to staxel's minimum requirements your computer might not be able to manage a full install of EF on top of Staxel proper. (This is not the end of the world. You just need to be selective about what you install. See the FAQ about removing content from EF for suggestions on what can go.)

I'm having problems getting it to load!
When the game first tries to launch after it detects a new mod it will run the content builder. This process only happens after an update to the vanilla game, an update to any mod you're using or if you change your mods. EF and all packs will make the CB process take a while. Run it and walk away for a while. On rare occasions it will fail to build. This usually occurs if a file the game expects to be there was removed or deleted somehow. This can happen with any mod, but is most likely to happen if you had some mods and uninstalled them.

Should Staxel tell you that the game couldn't launch because of an error:

1. Run Mod Manager (from the Steam launcher if you're using Steam to install your mods.)
   
2. Select Tools>Run Content Builder with Validation.

You should be able to load and run the game after this process. If this doesn't work for you: please visit the main Staxel discord. We don't bite and you'll get a much faster solution to your problem than posting here in the comments.

Ok. but why is this happening?

Technical type stuff follows in the least technical manner possible: Staxel runs a process before it loads the game to make sure that all the files it thinks should exist actually do exist, and checks for new files it didn't know about before (mods). If it finds new files it has to fit them into the game and part of that process is making sure there aren't conflicts that would make the game crash. Normally a mod only has a handful of items. Maybe even a couple hundred.

Vanilla Staxel has ~2000 items. EF with all packs has ~2500 items. (Yes. It's that big.)

Once you successfully content build the game writes itself a little note saying "these are all the files I know about. The next time I run if I find all of these files and don't find any new ones then I'm good to go!" and the game will load faster.

Unfortunately whenever a new item is added the game can't just say "Oh, I know those files. They worked before. They're cool. I just have to deal with these five new ones." It has to check those five new ones against every other file in the game to make sure none of those files conflict with the old ones. It also has to do a bunch of other stuff.

Which is all a very long way of saying it takes a while because EF is enormous.