SCOPE_IDENTITY returning null values sometimes - sql

Question

I've got a SQL query where sometimes the IDENTITY value from the INSERT [Form] in the first statement comes back as NULL and causes the rest of the statements in the batch to fail.
I included the second block of the procedure to indicate where it fails due to a conflict with the FK constraint on the table Form
Previously, it had been using SCOPE_IDENTITY, but I had changed it to use SQL Server's temp tables and an OUTPUT clause to see if it would alleviate the issue and it hasn't.
This procedure is being called from an ASP.NET webforms application, and the call is initiated by a Web API call running in that application.
Previously before this was ever made into a Web API call, it was initiated by a click event in the webforms application. Back then I would see this error occur every now and again.
With more and more use of the application and heavier loads, this seems to occur more frequently.
I checked and there are no triggers on the table that are firing off. I can't think of any way to replicate or track down the problem.
In most cases the procedure works fine, but every now and again it doesn't, and I'm unsure why. Sometimes I'll see a log of the error occurring multiple times in a row as the user attempts to save what they are working on. If they try enough times, it seems to work.
I've looked into using other forms of identity retrieval like ##IDENTITY and those won't work for what I need.
Is there something I'm missing?
ALTER PROCEDURE [dbo].[IC_Note_UpdateForm]
#FormID int = -1 OUTPUT, #ConsultFormID int = -1 OUTPUT, #PatientSignature bit, #DSPSignature bit, #Editable bit, #Narrative nvarchar(MAX) = NULL, #SignificantIssues nvarchar(MAX), #UserID int, #DSPID int, #FormTypeID int, #ServiceID int, #ApptID int OUTPUT, #LocationID int, #LoggedInUser int, #PortalId int,#ClientNotes nvarchar(MAX)
WITH EXEC AS CALLER
AS
SET NOCOUNT ON;
--This is needed for whatever reason in order to get the correct date submitted. Using the function call inline causes weird stuff to happen
DECLARE #DateSubmitted DATETIME = dbo.GetLocalTime(default)
DECLARE #count int
--See if a record exists for the Form
SELECT #count = COUNT(FormId) FROM Form WHERE (formID = #FormID OR (apptID = #ApptID AND apptID >= 1))
if #count > 0 BEGIN
UPDATE dbo.Form SET
FormTypeID = #FormTypeID,
patientSignature = #PatientSignature,
dspSignature = #DSPSignature,
editable = #Editable,
dateSubmitted = #DateSubmitted
WHERE
formID = #FormID
IF #Editable = 0 BEGIN
exec IC_NoteAudit_Insert #FormId, #DSPID, 'SUBMITTED'
END ELSE BEGIN
exec IC_NoteAudit_Insert #FormID, #DSPID, 'UPDATED'
END
END ELSE BEGIN
DECLARE #tempForm TABLE (FormId int)
INSERT dbo.Form (
PortalId
,userID
,dspID
,dateSubmitted
,patientSignature
,dspSignature
,editable
,approved
,dateApproved
,rejected
,formTypeID
,paid
,billed
,serviceID
,apptID
) OUTPUT inserted.formId INTO #tempForm
VALUES (
#PortalId
,#UserID -- userID - int
,#DSPID -- dspID - int
,#DateSubmitted -- dateSubmitted - datetime
,#PatientSignature -- patientSignature - bit
,#DSPSignature -- dspSignature - bit
,#Editable -- editable - bit
,null -- approved - bit
,null -- dateApproved - datetime
,null -- rejected - bit
,#FormTypeID -- formTypeID - int
,0 -- paid - bit
,0 -- billed - bit
,#ServiceID -- serviceID - int
,#ApptID -- apptID - int
)
--This was SET #FormId = SCOPE_IDENTITY() before and had the same NULL FK constraint occur
SET #FormID = (SELECT TOP 1 FormId FROM #tempForm)
END
--Move these out of scope of the IDENTITY retrieval
IF #count = 0 BEGIN
exec IC_NoteAudit_Insert #formID, #DSPID, 'CREATED'
IF #Editable = 0 BEGIN
exec IC_NoteAudit_Insert #formID, #DSPID, 'SUBMITTED'
END
END
SELECT #count = COUNT(FormId) FROM ConsultForm WHERE formId = #FormID
IF #count > 0 BEGIN
--See if a row exists for the ConsultForm
UPDATE dbo.ConsultForm SET
narrative = #Narrative,
significantIssues = #SignificantIssues
WHERE
consultFormID = #ConsultFormID
AND formID = #FormID
END ELSE BEGIN
DECLARE #tempConsultForm TABLE (ConsultFormId int)
INSERT dbo.ConsultForm (
PortalId
,formID
,dateOfService
,timeIn
,timeOut
,narrative
,significantIssues
,locationOfService
) OUTPUT inserted.ConsultFormID INTO #tempConsultForm
VALUES (
#PortalId,
#FormID -- formID - int
,null -- dateOfService - datetime
,null -- timeIn - datetime
,null -- timeOut - datetime
,#Narrative -- narrative - nvarchar(MAX)
,#SignificantIssues -- significantIssues - nvarchar(MAX)
,null -- locationOfService - nvarchar(MAX)
)
/*** Failure with FK constraint happens here, #FormId is NULL ***/
SET #ConsultFormID = (SELECT TOP 1 ConsultFormId FROM #tempConsultForm)
END ````

Answer 1

Which Version of SQL, seems like a bug in SQL. Can You use RAISERROR inside the SQL Code to make sure whether it is an issue in SQL itself.