The grid (core) · console.warn

unknown icon set '{name}'; falling back to arrows.

Printed by The grid (core), prefixed [lattice], since 1.39.0.

Warnings reference › iconSet:*

Identifier: iconSet:*
Raised by: The grid (core)
Since: 1.39.0

What happened

A conditional-formatting icon-set rule named a set that does not exist, so the arrows set is used instead. The rule still applies and the thresholds still work; the glyphs are not the ones asked for.

The fix

Use one of the built-in icon set names.

Reference

Covered in full at the API reference.