I agree the behavior seems erratic. It seems "Delete Hidden Effects" - one of the menu options - is being applied without your clicking that option. Styles.psp is a settings file and I'm not sure what triggers that file updating, nor what data is being retained within the document vs. the setting file. If you open a New document and Show All Effects, subsequent new docs show all the effects. However when you open docs with layer styles previously applied, or make changes to the list, those differences sometimes stick in newly opened docs, but not in docs that were open, or opened before the reset. Not at all ideal, but you could follow the below steps to have a button to click to Show All Effects. Again not ideal but easier than menu diving. I'll look into this more and file a bug or feature request when I can pin the behavior down. Open a New doc and Reset to Default List and/or Show All Effects so that the list looks the way you want. Without applying any style, nothing checked, click the New Style button on the right. Rename if you want and click OK. Now applying that full list of styles will be the last button in your Styles panel. Whenever you want to Show All Effects just click that button.
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