How many cables do you have running to the keymander. Since the keyboard is back lit it may be drawing to much power from the keymander. Try connecting a cable in the POWER port and wire that to a wall charger and see if that fixes the issue.

It could be that it has to see a PC connection to allow the SL button to function, but that seems like a very strange way to actuate lighting control.

Currently I have the power cable, Game cable connected to gamepad. Mouse and keyboard are connected and function fine. Everything works with the device as intended.

But if I put the keyboard into the PS4 by itself it will use the scroll lock button just fine. I thought Keyboard mode might fix the issue, but it doesn't. The button for the backlight only seems to work when either plugged into a pc or into the PS4 directly. So only when plugged into the keymander does the scroll lock not yield the on/off of the lights.

The PS4 recognizes keyboards so it will act like it does with a PC to some extent, which is why the button works. KeyMander makes the keyboard appear to the PS4 like it is part of the controller, so it will not see a keyboard when connected to KeyMander.

Here's a permanent solution I found online that keeps the keyboard on whenever the PC is on (in the case of KeyMander I'm guessing it will be lit whenever KeyMander has power connected):

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