Answer
Check whether the mandatory FND_WEBENDUSER_MAIN permission set is actually being used for basic Aurena access (rather than substituted entirely with a custom permission set), and confirm no permissions have been inadvertently removed or modified on FND_WEBENDUSER_MAIN itself. Missing permissions on this specific mandatory permission set is a known cause of exactly this kind of generic 'internalName' JavaScript error appearing on first page load in Aurena.