CN1 is a ribbon cable? Perhaps remove / reseat or even replace?

Can you measure your 5 volts and tell us what the reading is? Usually resets=low five volts=replace bridge.

Edit: I know someone said it was fine, but it takes 20 seconds to check.

Well, the easiest way would probably be to measure at said connection, CN2. This is the plug that is in the bottom left part of the top board (cpu board). It's a chunky white plug, not a ribbon cable. It has 6 pins on it. The one all the way to the right is pin 1, which is what we want. The one next to it is pin 2, which is ground. So take your meter, make sure it's on the correct setting for 5v DC, and put the red lead so it's touching the back of that plug all the way to the right. You want to make sure it's touching the metal part, not just the plastic. Then take your black lead, and put it on the back part of the pin next to it. Same thing with the metal part. Look at the reading. Tell us what it says. If it says 0, you're doing it wrong. Don't let the two leads touch while you're measuring. It won't hurt anything permanently, but it may blow a fuse.

5V issues are common reasons for resets, what happens to the LEDs on IO and sound board when it resets? Could be battery damage too, have you checked this article out?
http://www.pinballsupernova.com/images/Sega_Stern%20White%20Star%20Repair%20-%20PinWiki.pdf

I've fixed lots of issues with resets on Whitestar boards. In almost every case it was either connector J16 on the power driver board (right above the voltage regulator/heatsink at the top of the board) and/or CN2 on the CPU sound board directly above J16.

Try reseating both of these connectors first. Pull up on them a little and push back down. If this makes the resets suddenly go away, then you know you have a connector issue at one end or the other. I typically remove the boards, replace the header pins and replace the connectors at both locations.

Although Whitestar boards have an easy way to adjust the +5VDC, I've never had to adjust one yet. It's always been a bad connector. My feelings are that since J16 and CN2 are directly above the voltage regulator heatsink, the heat from the VR is causing the issue. It makes sense because the plastic connector housings for those two connectors are always so brittle they fall apart in your hands.

Perhaps it's time to send it to a pro.
I can take care of it if you'd like.

Does the board have any battery leakage corrosion?
Adjacent to the battery holder are the ROM, RAM, and CPU along with very fine delicate traces.
They are all subject to corrosion damage.
--
Chris Hibler - CARGPB #31
http://www.ChrisHiblerPinball.com/Contact
http://www.PinWiki.com - The Place to go for Pinball Repair Info

Get the game into test mode and see if it’s somehow making the slam tilt trigger. Could be a miswired switch causing a matrix issue (assuming this era game has a matrix, newer Stern do not)

Marc

Home Depot, Lowe’s, etc.
there is a correct way to wire a plug.
Duplicate the current wiring.
—
Chris Hibler - CARGPB #31
http://ChrisHiblerPinball.com/contact/
http://www.PinWiki.com - The new place for pinball repair info

I would cover those wires with electrical tape or a wire nut to make sure you don’t get a short down the road.

How the flying heck are you working on a pinball machine and unable to wire a plug. I would YouTube and Google search such a simple problem before posting here.

What's next, you going to claim the game is cursed?

There is a chip right under the batteries I would reseat it as well caused odd behavior in my game (actually found battery acid under it) but others have fixed just by getting it tighter. My symptoms would be a few targets would reset the game similar to your Issue

This, and I've had a Monopoly reset on me because I didn't have good volts at the outlet. Stern needs 105v or above to run smooth, which can also be compromised while running an AC or fridge on the same circuit.

To clarify, all you need is some kind cord that has the correct three prong end, and is long enough. We use 12' cords but anything that will reach the outlet is fine. You can get them at a hardware store, or if you can't get to one for some reason you can order them online. You should be able to find one that's just the one end, with the wires sticking out the other. If you can't, buy a normal cord, and just snip off the end that isn't the three prong plug, and use a set of wire strippers or cutters to remove the outside plastic covering for the end 4 inches or so. Assuming you buy it new in the USA, there should be three wires inside, one white, one black, one green. All you have to do is solder the ends just like they are inside the machine. The easiest way to do it is to cut the existing power wire inside the machine about 4 inches from your EMF filter. Pull out the old cord from the back, and thread the new one in. Then one by one, desolder the old wires and resolder the new ones on.

https://pinside.com/pinball/forum/topic/replacing-line-cords-plugs-wall-sockets-vids-guide