"Spare" pins on the GPIO connector

[2600Sam]

They do have posted on their Github

Why SDA0(pin 0 in BCM mode) pin can’t be used?
Since this pin is used to detect the startup pin of the system in order to control the power on/off on the PCBA board. If this pin is used, it may cause the CrowPi2 to shut down.

and an FYI from there as well

Release information about CrowPi2 image
We have not released the CrowPi2 image currently, therefore, backup your image after receiving CrowPi2 yourself! Any news about releasing image, we will update to our official website

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Yeah for buggy early hardware