the date pattern "{pattern}" contains '{ch}', which is not a supported token, so it is rendered as text. Quote it as a literal to silence this. Supported: {tokens}.

Warnings reference › date.pattern.token:*

Identifier

date.pattern.token:*

Raised by

The grid (core)

Since

1.4.0

What happened

A letter in a date pattern is not one of the tokens the formatter implements - zzz for a zone, QQ for a quarter - so it is emitted as literal text and the letters themselves appear in the cell. Punctuation and spaces are legitimately literal and say nothing.

The fix

Use one of the supported tokens, or quote the letters as a literal if they are meant to be text.

The smallest fix

format: { date: "yyyy-MM-dd 'UTC'" }

Reference

Covered in full at the API reference.