Undervoltage when using USB power on ControlBlock

[normal]

I am using a 5V 2.5A power adapter for my Raspberry Pi 3 running RetroPie 4.1, and it runs fine powering it directly with a fairly high overclock of 1300. However, when I use the same adapter or any other (such as a genuine Samsung fast charging adapter) on the USB power slot in a ControlBlock v2, I get constant undervoltage warnings immediately at boot even at stock speeds. I have two sets of buttons wired with the arcade configuration and no LED or power switch wired yet. Setting over_voltage to 8 does not solve it. What can I do?

[normal]

I measured voltage on the testpads on the bottom and the exposed GPIO pins on the ControlBlock and get more than 4.77V. That should be more than enough but I still get the thunderbolt constantly. I get it less often if I unplug all USB devices and ethernet but it still occurs.

[petrockblog]

I made the observation in the past that using a high-quality USB cable also plays a major role: A thicker cable leads to a lower voltage drop when the Rai needs a lot of power. You might want to try out another cable.