For 故事 which uses the definition "story", the book I'm reading states the pinyin is "gùshì" but the PLC dictionary says "gùshi" for that definition. Google Translate also agrees with the book pronunciation. Why does the PLC dictionary disagree?
It could be that the pinyin line in the book you're reading or Google's pinyin was automatically generated, or that the book is from Taiwan, where this losing of tones in the second syllable doesn't occur (to my knowledge).
I see that 故事 pronounced "gùshì" can also mean something different, "old practice, routine".