I’ve read through this post V5.99 Fill Zones not showing a filled
I have a sidepanel board which should have ground fills on top and bottom layer, but suddenly KiCAD isn’t filling the copper pours any more.
preamp_front-panel.kicad_pcb (153.8 KB)
I’ve added the GND net manually and assigned the vias to that net, but that doesn’t seem to be enough.
KiCad considers areas with no connection to a pad to be isolated, and this zone is set to remove isolated islands (which is the default). Your design has no pads, so everywhere is considered isolated even if you add vias. To get this zone to fill, either add a pad on the GND net inside the area, or change the zone settings to never remove isolated islands.
Note for others: This feature is not available in KiCad 5.1.x and earlier (5.99 used by OP is the nightly development snapshot intended to allow users to more easily help test what will become the future of KiCad)
More details about how zones in stable work (nightlies generally work the same but have additional features not listed in that article): How to create a power plane (using zones)