An internal error occurred. Editing functionality may be limited

That could be an error in one of the IB items (as a wrong or corrupted connection to an IBOutlet in a controller).

Do you get any error (red or yellow sign) in IB ?

Some questions at this stage:

- Is it an older project (created with an older version of XCode) ? Did you test with a brand new project ?

- Have you several versions of XCode installed ?

- Does the project compile OK ?

- Can you find some error report ? Anything in Issues navigator ?

You could check all the steps to clear such eror here:

https://stackoverflow.com/questions/33456411/ios-project-showing-error-an-internal-error-occurred-editing-functionality-may

Notably this one:

I was getting this error on Xcode 11.4. I tried all of the above suggestions and none of them worked. I am posting my fix in case it will help someone else. I was using the legacy build system for my project since I had options that were not yet supported with the latest build system. Xcode 11.4 now supports those options. I the value for

BuildSystemType

to

Latest

in all of WorkspaceSettings.xcsettings files and then this error went away.

    <key>BuildSystemType</key> <string>Latest</string>

Get there with Xcode Files-> Project/Workspace Settings

- Were all XCode components correctly installed?

As a last resort, you could try to reinstall XCode.

When you get the "internal error" message in Interface Builder like this it typically means that one of the background processes has crashed for some reason. This will usually create a crash report containing diagnostic info.

If you can still recreate the issue, please do so. In that banner that shows the "internal error" message there should be a button to the far right. If you click that button it should reveal a folder with the crash report and other diagnostic files. This should also include the storybard that's causing the issue.

Alternatively you can look for the crash log in the Console.app under the "Crash Reports" section in the sidebar. You'll be looking for a crash report from a process name like "IBAgent" or "ibtool".

If you can find any of those please file feedback using the Feedback Assistant and attach the files to the feedback. It's also extremely helpful if you can attach the storyboard that's causing the issue, but I understand this isn't always possible.

For more info on Feedback Assistant see: https://developer.apple.com/bug-reporting/

Hope this helps.