grid command does nothing on third monitor

[hitsfromdabong]

My problem is simple: When I try to use the "grid" command to resize a window on my third screen simply nothing happens. No problem with the other two screens though.

Im using:
macOS Mojave, version 10.14
macBook Pro (retina, 15", late 2013)

Slate version: 1.0 (1.0.25)

Monitor setup is:
HP w19b/w19e (via hdmi -> vga -> monitor; this is the problematic monitor)
Samsung U28E590 (via displayport; no problem resizing)
internal Retinal display (also no problem)

Furthermore no problems during grid configuration.

.slate file:

bind w:cmd grid padding:5 0:6,3 1:8,4 2:6,3