PHP Startup: Unable to load dynamic library

The folder is missing. However for fun I pushed the site to a clean Heroku repo and experienced a lot of issues.

I am running a test on a Heroku stack:
remote: -----> Bootstrappingā€¦
remote: -----> Installing platform packagesā€¦
remote: - php (5.6.28)
remote: - ext-mbstring (bundled with php)
remote: - apache (2.4.20)
remote: - nginx (1.8.1)
remote: -----> Installing dependenciesā€¦
remote: Composer version 1.2.4 2016-12-06 22:00:51

Issue is very similar to this: Panel keeps logging me out

And the console shows the unexpected error for <

Additionally, If I do not explicitly tell it composer to install ext-mbstring I can not reach the panel.

To login in I must click the login button twice.

I am running Kirby 2.4.1.

Site can be found here:

https://gentle-peak-44833.herokuapp.com

Gist:

I did go back to my testing server and drop in a version running off of Kirby 2.3.1 and it works perfectly.