Won't boot if I/O ribbon cable is plugged; replaced cable, same error

After a whole lot of due diligence, I diagnosed that it was the I/O flex ribbon cable causing my MBP (13” retina early 2015) from booting (couldn’t even get the apple logo, only the sound and a brightness adjustment on the black screen). However, if I unplugged that i/o ribbon cable, it booted and worked fine, albeit no wifi/usb/bluetooth.

So I bought a new I/O ribbon cable from iFixit, replaced it, and everything worked just fine until the laptop’s first full charge. Now suddenly it won’t turn on again unless I unplug the ribbon cable!

Super weird and super bummer because I was very excited to have it working smoothly again. Could this be an issue with the I/O board itself? Or something else?