InDesign SDK | Need help with hyphenation

As you can see in the screenshot above, first textframe (on the left) is hyphenating the word "Clean-cut" incorrectly. The text is written in a custom language which uses sample hyphenator plugin from "sdksamples/hyphenator".

The second textframe (on the right) is hyphenating the word correctly without double dashes which is written in built-in language "English: USA".

I wonder why the sample plugin is working incorrectly when coming to hyphenating the words with dashes in them.

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Here I will leave some code snippets from that plugin and debug logs:

HypAdapter.cpp, HypAdapter::findHyphenationPoints function has this, maybe something is going wrong here:

// Scan the characters and selectively generate hyphenation points.
for (int32 i = 0; rWord.CharCount() > 0; i++, rWord.RemoveFirst())
{
	Hyp::HyphenQuality hyphenQuality = IHyphenatedWord::kNoHyphenPoint;
	switch (rWord.First().GetValue()) {
	case kTextChar_HyphenMinus:
	case kTextChar_UnicodeHyphen:
	case kTextChar_FigureDash:
	case kTextChar_HorizontalBar:
	case kTextChar_EmDash:
	case kTextChar_EnDash: {
		hyphenQuality = IHyphenatedWord::kHardHyphenPoint;
		break;
	}
	case kTextChar_DiscretionaryHyphen: {
		hyphenQuality = IHyphenatedWord::kDiscretionaryHyphenPoint;
		break;
	}
	case kTextChar_Solidus:
	case kTextChar_ReverseSolidus:
	case kTextChar_Ellipse:
	case kTextChar_FlushSpace:
	case kTextChar_EnSpace:
	case kTextChar_EmSpace:
	case kTextChar_FigureSpace:
	case kTextChar_PunctuationSpace:
	case kTextChar_ThinSpace:
	case kTextChar_HairSpace:
	case kTextChar_HardSpace:
	case kTextChar_ZeroSpaceBreak: {
		hyphenQuality = IHyphenatedWord::kUnpreferredHyphenPoint;
		break;
	}
	}
	if (hyphenQuality == IHyphenatedWord::kNoHyphenPoint) {
		continue;
	}
	hyphenationPoints.push_back(Hyp::HyphenationPoint(i, hyphenQuality));
}

From logs, I can see this:

HypDiagnostic:TraceHyphenatedWord("Clean-cut")-->In
 word(ascii)="Clean-cut"
 nNthPoint, hyphenIndex, hyphenQuality
 0, 5, 90
 hyphenatedWord="Clean--cut"
HypDiagnostic:TraceHyphenatedWord()-->Out

Will be waiting for your response, thanks!