Q:

REST API: Operation is not valid due to the current state of the object

I am having issues accessing data from a DAC that has any amount of customization with it. I have a DAC with a few more complicated modifications, so I will start with the simple one. I have modified the External Reference field of SO.SOOrder. This is the only change to the DAC.
Originial Attributes
[PXDBString(40, IsUnicode = true)]
[PXUIField(DisplayName = "External Reference")]

Customize Attributes (Replace Original)
[PXDBString(40, IsUnicode = true)]
[PXUIField(DisplayName = "Some Text Here")]

Now, when I attempt to access any SalesOrder via the REST API:
GET https://site.acumatica.com/entity/Default/17.200.001/SalesOrder/SO000123

The following error is returned:
{
    "message": "An error has occurred.",
    "exceptionMessage": "Operation is not valid due to the current state of the object.",
    "exceptionType": "System.InvalidOperationException",
    "stackTrace": "   at PX.Api.ContractBased.EntityService.FillEntityImplWithKeys(String version, String name, EntityImpl entity, String[] keys)
   at PX.Api.ContractBased.SystemContracts.V2.SoapFacade.PX.Api.ContractBased.IRestGate.FillEntityImplWithKeys(EntityImpl entity, String[] keys)
   at PX.Api.ContractBased.SystemContracts.V2.RestController.CreateEntityFromKeys(String objectName, String idsString)
   at lambda_method(Closure , Object , Object[] )
   at System.Web.Http.Controllers.ReflectedHttpActionDescriptor.ActionExecutor.<>c__DisplayClass10.<GetExecutor>b__9(Object instance, Object[] methodParameters)
   at System.Web.Http.Controllers.ReflectedHttpActionDescriptor.ExecuteAsync(HttpControllerContext controllerContext, IDictionary`2 arguments, CancellationToken cancellationToken)
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at System.Web.Http.Controllers.ApiControllerActionInvoker.<InvokeActionAsyncCore>d__0.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at System.Web.Http.Filters.ActionFilterAttribute.<CallOnActionExecutedAsync>d__5.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at System.Web.Http.Filters.ActionFilterAttribute.<CallOnActionExecutedAsync>d__5.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at System.Web.Http.Filters.ActionFilterAttribute.<ExecuteActionFilterAsyncCore>d__0.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at System.Web.Http.Controllers.ActionFilterResult.<ExecuteAsync>d__2.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at System.Web.Http.Filters.AuthorizationFilterAttribute.<ExecuteAuthorizationFilterAsyncCore>d__2.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at System.Web.Http.Controllers.ExceptionFilterResult.<ExecuteAsync>d__0.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at System.Web.Http.Controllers.ExceptionFilterResult.<ExecuteAsync>d__0.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at System.Web.Http.Dispatcher.HttpControllerDispatcher.<SendAsync>d__1.MoveNext()"
}

Now, I'm not certain if this is occurring because of my DAC modification or not, but I cannot find anything else linking this and my other troubled DAC CustomerLocation to the same error message.
Where do I go from here to identify what what the bad state is?

A:

Since this screen contains multiple key fields (Order Type and Order Nbr.), you need to put them all in the URL.
GET https://site.acumatica.com/entity/Default/17.200.001/SalesOrder/SO000123

gets changed into if this is a type SO Sales Order
GET https://site.acumatica.com/entity/Default/17.200.001/SalesOrder/SO/000123

SO is order type and 00123 is Order number

