There is a know issue (at least it was in early code) that if you adjusted the GI brightness settings it would cause the side exterior cabinet lights to not turn on and other weirdness.

If you test the LED strip with a 9v battery with the machine turned off and it is truly out, the part that is lighting up the exteriors sides is a simple LED strip you can probably get for $5 on https://www.aliexpress.com/wholesale?catId=200002296&initiative_id=AS_20180428135507&SearchText=white+led+strip

What version of code are you on and are you using a ZOTAC or the minpc?

I would also try moving the power connection to the CPU (which ever one you have) to a different USB port.

This can't hurt

Did you switch them around to different I/O boards? I'd still try or try the above.

Everyone should probably check this. Had no problems for many months and then flipper mayhem.

Before you do anything check the flipper button switch alignment (centered or not) on the cabinet and tightness of screws holding it in place.

There are other threads to try.

https://pinside.com/pinball/forum/topic/get-away-from-her-you-bitch-alien-club-all-members-expendable/
https://pinside.com/pinball/forum/topic/weyland-yutani-dedicated-to-keeping-3-alien-specimens-alive/
https://pinside.com/pinball/forum/topic/alien-pinball-official-game-thread/

https://pinside.com/pinball/forum/topic/weyland-yutani-dedicated-to-keeping-3-alien-specimens-alive/page/4#post-4417562

Looks like those don't work anymore. The instructions are valid though

Try this

http://www.rs-pinball.at/alien/

1. Check the connectors by wiggling them on the small zeno board as you cycle the test for the tongue (I forget the name right now). If you can get the tongue to stop then obviously reseat the wire in the connector.
2. While cycling in the same test try it with a ball and adjust the Potentiometer (small sunken screw) with a jewelers screwdriver clockwise until it can drop the ball. This can take some fiddling as if I remember correct if you go too far it will lose power.
xeno_board_small (resized).png

In my image the screw marked with the red arrow is to the right of my yellow thunderbolt on the raised board. Like I said you will need a jewelers screwdriver or equivalent.

xeno_board_small (resized).png

Also, did you try the turning the screw clockwise gradually and testing as you go? because on mine more power and it would drop the ball. That is why I mentioned it. It worked for me.

Power (resized).jpg