I'm attempting to modify a Quote Layout using Salesforce Classic UI to add and remove a couple of buttons. In the past this worked just fine.
The main thing that changed between then and now is that I attempted to uninstall a managed (beta) package, found that a button from the package was still being referenced in the quote layout. I then went into the Quote layouts under Setup -> Customize -> Quotes -> Page Layouts -> click Edit link next to Quote Layout
I now receive the message "Data Not Available" where before I would be able to edit and save the default Quote Layout. I've been able to successfully add new Layouts, but attempting to edit the newly added page layouts results in the same error message.
I'm using a Dev Org, and have verified that my account is still marked as a System Admin. I've tried editing the layout from different locations, like the "Where Used" feature (same error). I've also tried adding permissions as listed here: https://help.salesforce.com/articleView?id=quotes_template_create.htm&type=0
The permissions listed there seem to be for the quote template, and not the page layouts though.
I am still able to edit other layouts, such as those for Opportunities. Another strange thing is that I thought there were 4 layouts before (marked with Marketing, Sales, Support, and one Default), now there is only the default. None of the layouts appear in the Recycle Bin (I checked the box to 'keep data for 48 hours' during the package uninstall attempt too), and the layout doesn't seem to be gone entirely because I can still access the Quotes list/page and the custom button is still there on the Quote page too.
Any assistance/information around the following 2 questions is much appreciated.
Is there some other permissions that I need to be able to edit page layouts for quotes (not seeing documentation or questions like that, yet)?
Alternatively, is there some way that I can do a "factory reset" on my dev org to get it back to a brand new "clean" state?