Why display settings don't show up and revert to the default
                    Why is it that sometimes when I open Zotero, all the display settings I previously configured don't show up and revert to the default settings? For example, I set it to display the volume and issue number, but the next time I open it, the volume and issue number are not displayed. This has happened twice already. The last time it happened, I uninstalled all the plugins and reinstalled them, and then set the display labels again. But today when I opened it, it reverted to the default settings once more. What on earth is causing this, and how can I fix it?                
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It might help if you provide some screenshots to show what you're referring to.
It sounds, though, like you're ending up in Troubleshooting Mode (which is indicated by a label in the toolbar), which could cause display settings not to be followed until you restart. As for how you're ending up in Troubleshooting Mode, if Zotero crashes (or a close is interpreted as a crash) several times in a row, that happens automatically. You should pay attention to what exactly you're doing before this happens.