Why did a gap cost me the stop-honoured component?

Because bar data cannot tell the difference between price trading through your stop while you watched and the market gapping past it. The component reads both as a breach.

Stop honoured is computed from how far price went against you, measured against your planned stop distance. Reaching exactly your stop is a pass; going beyond it is a fail.

A gap or a bad fill can carry a trade past its stop on a trade you managed perfectly — you were stopped out at the first available price, which was worse than the level you set. The bars show price beyond your stop, and there is nothing in them that distinguishes that from sitting there while it ran.

This is a known limit rather than a bug, and it is worth knowing before you take the component personally. If a component seems wrong on a specific trade, the per-trade breakdown in the Journal's Grade column will show you which of the five it was.