I am working on a project where the switch is controlled by the M5 PIR SENSOR.
When I power the ATOM from USB everything works fine, when I power it with a 12V 3A PSU thought the RS485 voltage converter the PIR begins malfunctioning (fake triggers).

I checked the voltage of the two groove outputs (from the hub and from the atom lite) under USB and 12V power. As long as USB is connected, the interfaces shows a quite stable 4.98V.
When the USB is unplugged, leaving only the 12V power source, the voltage drops to 3.3-3.28V, if the atom is removed it goes back to 5V
I guess this is causing the PIR to misbehave, since it requires 5V.

What´s wrong?
According to labels on the components and to the HUB schematics, I expect 5V 2A from the DC/DC converter.

Based on your photo's you haven't connected the 12V to the correct pins of the RS485 connection.
12V needs to be connected to the RS485's red and black pins.

Based on sticker of the HUB, red is 12v and black is gnd.

Hope this helps

Jason