<rdar://problem/40062065> <https://trac.webkit.org/r231299> or maybe <https://trac.webkit.org/r231014> made it so that com.apple.WebKit.WebContent.Development is no longer getting signed with the com.apple.security.cs.disable-library-validation entitlement entitlement.
*** This bug has been marked as a duplicate of bug 185241 ***