Webviewpage Model returns Nothing when deployed on web server - asp.net

Question

I am creating an ASP.Net website with VB.Net as code behind and this is the error that appears from the published version on a web server (this does not appear when run directly from the code or from the published version on the IIS server):
error message screenshot
This is a snippet from the controller:
Function Index(ByVal pSurveyName As String) As ActionResult
Try
If IsNothing(pSurveyName) Then
Return New HttpStatusCodeResult(HttpStatusCode.BadRequest)
End If
Dim l_question As Object = GetQuestion()
Return View(l_question)
Catch ex As Exception
Call ExceptionHandler(ex)
Return View()
End Try
End Function
Function GetQuestion() As Object
Dim l_questionnaire = Session("ActiveQuestionnaire")
Dim l_surveySession = Session("SurveySession")
Dim l_redirectQueue = Session("RedirectQueue")
Dim l_sessionAnswers = Session("SessionAnswers")
Dim l_CurrentQuestion As CurrentItem = New CurrentItem
Dim l_Choices As List(Of Choice) = New List(Of Choice)
Dim l_TempDBQuestions = db.Questions
Dim l_TempDBChildQuestions = db.ChildQuestions
Dim l_TempDBChoices = db.Choices
Dim l_tempFiltered_Q
Dim li_questionnaireID As Integer
Dim li_questionCtr As Integer
Dim li_total_NoOfQuestion As Integer = 0
Dim li_resultCount As Integer = 0
Dim li_childQID As Integer = 0
Dim ls_prevAnswer As String = ""
Dim ls_err As String = ""
Try
li_questionnaireID = l_questionnaire.ID
li_questionCtr = l_surveySession.QuestionCtr
If Session("Back") = False Then
li_questionCtr = GetQuestionCtr(NEXT_QUESTION, l_surveySession, l_redirectQueue, l_sessionAnswers,, ls_prevAnswer)
Else
Dim l_current = Session("CurrentQuestion")
li_questionCtr = GetQuestionCtr(PREVIOUS_QUESTION, l_surveySession, l_redirectQueue, l_sessionAnswers, l_current, ls_prevAnswer)
End If
l_tempFiltered_Q = l_TempDBQuestions.Where(Function(q) q.QuestionnaireID.Equals(li_questionnaireID) And q.QuestionOrder.Equals(li_questionCtr))
li_resultCount = l_TempDBQuestions.Where(Function(q) q.QuestionnaireID.Equals(li_questionnaireID) And q.QuestionOrder.Equals(li_questionCtr)).Count
If li_resultCount = 0 Then
l_tempFiltered_Q = l_TempDBChildQuestions.Where(Function(q) q.QuestionnaireID.Equals(li_questionnaireID) And q.QuestionOrder.Equals(li_questionCtr))
Session("FrmChildQuestions") = True
Else
Session("FrmChildQuestions") = False
End If
For Each item In l_tempFiltered_Q
'item could be from Questions or ChildQuestions
If li_resultCount = 0 Then
Session("IsNextQuestionChild") = item.IsNextQuestionChild
End If
With l_CurrentQuestion
.ID = item.ID
.QuestionnaireID = item.QuestionnaireID
.QuestionOrder = item.QuestionOrder
.Description = item.Description
.AnswerType = item.AnswerType
.AllowMultipleAnswers = item.AllowMultipleAnswers
.QuestionNo = item.QuestionNo
.Required = item.Required
.TempAnswer = ls_prevAnswer
End With
Next
If l_CurrentQuestion.AnswerType = constants.MULTIPLE_CHOICE Then
'Get Choices
Dim li_questionID As Integer = l_CurrentQuestion.ID
If li_resultCount = 0 Then
l_Choices = db.Choices.SqlQuery("select * from Choices where ChildQuestionID = " & li_questionID & "").ToList
Else
l_Choices = db.Choices.SqlQuery("select * from Choices where QuestionID = " & li_questionID & "").ToList
End If
Session("Choices") = l_Choices
End If
If Session("TotalQuestions") Is Nothing Then
li_total_NoOfQuestion = db.Database.SqlQuery(Of Integer) _
("select max(a.MaxOrder) from(select max(QuestionOrder) " &
"as MaxOrder from Questions union select QuestionOrder from " &
"ChildQuestions)a").FirstOrDefault
Session("TotalQuestions") = li_total_NoOfQuestion
End If
With l_surveySession
.QuestionCtr = li_questionCtr
End With
Session("SurveySession") = l_surveySession
Session("CurrentQuestion") = l_CurrentQuestion
Session("Back") = False
Return l_CurrentQuestion
Catch ex As Exception
Call ExceptionHandler(ex)
End Try
End Function
And this is from the view:
#ModelType Survey_App.Models.CurrentItem
#Code
ViewData("Title") = "Index"
Layout = "~/Views/Shared/_Layout.vbhtml"
Dim l_choices = Session("Choices")
Dim l_activeSurvey = Session("ActiveSurvey")
Dim ls_tempAnsType As String = Model.AnswerType.ToString 'this is the line indicated in the error msg
Dim ls_temp As String = ""
Dim ls_tempAnswer() As String = Nothing
Dim li_totalQuestions As Integer = 0
li_totalQuestions = Session("TotalQuestions")
Dim ls_POSTAction As String = vbNullString
The error appears some time (maybe 10-15 seconds) after going through the home page but not always immediately. I also tried some debugging and it looks like the session variables also return nothing after that some time.