After applying I received instructions from a recruiter and completed a several hour long code assessment project. Two weeks later they sent me a canned rejection email with no reason.

DO NOT DO THE TAKE HOME ASSIGNMENT!! IT'S UNFAIR INTERVIEW PRACTICE. Taking the take home assignments means you work for 4 - 6 hours for free, and competing with 10 other engineers who are doing the same thing. They will nitpick on your project and reject it, bc another one did it slightly better than you. You encourage these companies to continue this unfair practice by agreeing to do the home assignment, stop taking it and these companies will stop requiring it.