Do not follow an em dash with a comma.

The comma directly after the em dash is mechanically detectable, but the punctuation change remains preview-only.

Example

[Verse]
A word—, then silence

[Verse]
A word—then silence

The fix

In the workbench this finding carries one control, labelled Remove the comma. The change is contextual, so it is previewed as a diff in your document first and applies only when you confirm it.

Source

The guideline this rule enforces, as cited on every finding it reports: