Looks like a false positive in the triggering logic. Just to be sure, did you change the triggering heuristics in flags? If your chrome://flags#reader-mode-heuristics is "Appears to be an article", then it's using the Adaboost model, which should be the default.

I tried to reproduce it locally, but the classification result is NOT to show the prompt, which is correct.

adaboost_classification = {
   "blacklisted": 0,
   "derived_features": [ 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 1.0, 1.0, 0.0, 0.0, 0.0, 1.0, 3.0, 167.0, 686.0, 0.2434402332361516, 20.46948949045872, 23.643180835073778, 559.0 ],
   "distillable": 0,
   "features": {
      "anchorCount": 167,
      "elementCount": 686,
      "formCount": 3,
      "isMobileFriendly": 0,
      "mozScore": 20.46948949045872,
      "mozScoreAllLinear": 559.0,
      "mozScoreAllSqrt": 23.643180835073778,
      "openGraph": 0,
      "passwordInputCount": 0,
      "textInputCount": 2
   },
   "long_page": 0,
   "long_score": -0.6895042893142644,
   "score": -0.13034317356566089
}

Sorry, I forgot to turn JS back on from last debugging session.

With JS on, the classification matches the symptom.

adaboost_classification = {
   "blacklisted": 0,
   "derived_features": [ 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 1.0, 1.0, 0.0, 0.0, 0.0, 1.0, 3.0, 177.0, 731.0, 0.2421340629274966, 128.03578826196147, 180.08871649031806, 3560.0 ],
   "distillable": 1,
   "features": {
      "anchorCount": 177,
      "elementCount": 731,
      "formCount": 3,
      "isMobileFriendly": 0,
      "mozScore": 128.03578826196147,
      "mozScoreAllLinear": 3560.0,
      "mozScoreAllSqrt": 180.08871649031806,
      "openGraph": 0,
      "passwordInputCount": 0,
      "textInputCount": 2
   },
   "long_page": 1,
   "long_score": 0.18815486307294982,
   "score": 0.21965375368971324
}

The mozScore* features are too high, due to the swipeable article snippets in div.slick-slider. One possible fix is to disregard texts inside <a> when processing <p>, but this can be too costly to compute.

Thanks for looking into this. FWIW my chrome://flags#reader-mode-heuristics is "Default" and I get the reader mode prompt every time.

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