Why is my I-526 case taking much longer to be processed than cases with the same project?

It appears while most cases are taking about two years, some are taking longer. It seems that other than a mandamus action, there may not be much one can do about the slowdown in adjudications.

USCIS is notorious for these delays. I would not worry that this reflects on the ultimate approval of your I-526. I would recommend that you consult with your investment immigration attorney.

Try to reach out to your congressperson, but start with the regional center to see if they have ideas. It could be that you have a slower case officer or your source o funds is more complicated.

If you are still within the processing time, then there is nothing you can do. USCIS seems to group I-526s for the same project, but there is really no way of knowing what they do with every individual case.

Some officers work faster than others. Unfortunately, it sounds like your case got assigned to one of the officers who are a bit slower or happen to have cases that require more time to process.