Arduino reset after press PB

Hi folks,
This is my schematic which is very simple. I have few PBs that I have connected through some pull up resistors to digital pins. When I press a PB, a message is sent to LAN through W5100 module.

Everything was working well until recently. Now, very randomly, if I press a PB, it causes reset.

Link to Schematic

The power supply is an unknown Chinese 12+ model and ( IMO ) can handle excesses current consumption.

Any idea why this is happening?

The schematic does not show how the switches are actually wired, and we need to know what the state of the pin is, when the button is pressed, to make sense of your post.

How can an input pin ever be LOW in that configuration?

Why are you using 1K resistors?

Well, for 1k resistor, it's a typo. Sorry for that. I'm using 10K resistor and I corrected the schematic.
For the wiring part, the board is inside a aluminum enclosure and placed in a industrial panel. PBs are placed on the front door of the panel and wired to the phoenix contact terminals on the board ( C2 ). The other side of the PB is grounded.

So what is the Arduino switching when you push those buttons?
Anything with motors and it will be the interference they kick up that is resetting the Arduino not the push button.

Do you still get a reset with the Arduino switching nothing?