Issue with Serial Port Connections but only for certain devices

This past week we have encountered a problem that we have not seen before and I was wondering if you guys would be able to point us in the right direction.

A new application was created by a colleague and a few devices were created/loaded up with our most recent code-base. However, upon start-up of the device there was an error which basically boiled down to the serial port being open but not being able to read any data.

We have other devices successfully running our updated code-base, but when I tried creating a new application + pushing the code-base + adding the UART configuration environment variable I also had the same issue as the other application.

Through much testing we have ruled out electrical issues and software issues. We are wondering if there is some configuration that we may be missing or if you guys have any other insights.

We look forward to your help.

Device Type: Raspberry pi 3
ResinOS Version: 2.7.5+rev -> Issue found both with production and development devices
Other Relevant components: This is happening on the connection between a pi and a custom-made smoothie board


the configurations for the RPI3 can be found here:
and here:

You can also try this project out and see if it works for you:

Let us know if that helps.