@FFurious,

This honestly sounds as thought the connections are not wired properly. As you have a V1, make sure that the traveler wires are lined up between the two switches. The main unit is the unit that actually dims the light, while the satellite only sends dimming signals to the main switch. If the wires were crossed, this would explain why the brightness increase button did the opposite.

Do you have a diagram of how you have everything connected, we can try to help out - but I would first try to match the traveler wires between units as this would be the expected behavior.

  @FFurious,

That difference in setup is the key to the problem it seems. The load on the second switch is what is supposed to pass power to the fixture.

This blog: https://mrelectrician.tv/three-way-switch-wiring-diagrams/ had a great explanation of your exact setup, where both are fed into the same box.  As your wiring is set up right now, I do not believe that the switch will work as a three-way in this situation in its officially supported configurations; however, I would definitely recommend getting an electrician over, as the wires to set the switch up may be present but may have been stashed in the back of the box or may have changed to a different type of wire(traveler/line) and not marked as such.