The grid (core) · console.warn

source.mode "derived": union source "{label}" has no grid and was skipped.

Printed by The grid (core), prefixed [lattice], since 1.51.0.

Warnings reference › source.derived.union.missing.*

Identifier: source.derived.union.missing.*
Raised by: The grid (core)
Since: 1.51.0

What happened

One entry of the union names no grid, so it contributes no rows. The entry is kept in the list - so its label stays reserved - and the other parents union normally.

The fix

Give the entry a grid, or remove it from from.

Reference

Covered in full at the API reference.