If you have an app that won’t open or save, and you haven’t messed with it with git, then that’s an Anvil issue! Drop us a line at support@anvil.works with the app if, or a link to the app in the Editor (not the published version, the URL when you open it in the Editor) and we’ll take a look.
Very interested in errors that occur in normal but not incognito - can you do the same, please, but with a copy and paste of what appears on your JS console, and if you can also the Network tab of the browser dev tools when you try to save?