Sprockets error Sprockets::NotImplementedError: Custom asset_path helper is not implemented
I suggest, that the main problem is in sprockets version. in my rails 4.2.6 project i use sprockets 3.6.0, and in your Gemfile.lock snippet you use <3.0 version.
Just like an a test, you may update rails to 4.2.6 and try out fresh sprockets 3.6.0 + sprockets-rails 3.0.1 and fresh sass-rails 5.0.4 and sass 3.4.22 gem. I really do not know which one of this updates will help, but, I think it should work.
I don't know if this qualifies as an answer or not, but I wound up just pulling down my production Heroku repo and confirmed everything precompiled. I then slowly upgraded all my gems and everything continued to precompile properly. I guess I'll never know what caused this. Thanks to those who contributed.
You can easily overcome this problem. Although your current problem is more a version related problem and not sure if you bundle update properly. But there is alternative solution. Try installing the following gem: