Hi @Sharalene,
I don’t really see how Prism could be causing that. Usually oddities like that, from my experience, are when you use sync options and there are file permission issues which don’t let Obsidian to save options correctly. You could try going to your vault, into the .obsidian folder and making a backup of the appearance.json then deleting it. Upon restarting Obsidian and opening that vault your Appearance tab in Settings should be reset and the appearance.json file will recreate itself. See if setting your settings again and restarting helps this at all.
Alternatively, see if this still happens when you disable all plugins but Style Settings then restart Obsidian, set your settings up as you want them and restart again.
P.S. Also see if there are any file duplicates in the .obsidian folder. You should be safe to remove the ones mentioning conflict or -1 or something like that.