Excel VBA Screenupdating False Infinite Loop - vba

Question

I have a function that maps data from one sheet (where it has been copied) to another which is then used for further analysis. When I run the code with screen updating on it always works fine. When I turn screen updating off the code gets stuck in an infinite loop in the last part of the sub (highlighted in bold - it is the inner most loop of the final section of code). If you then debug the code and re-start it continues normally and finished the code. If left it will never end, but next time will work fine:
Sub simsMap()
Dim simsCol As String
Dim mapCol As String
range("A5:OP253").ClearContents
range("S1:OP1").ClearContents
range("S4:OP4").ClearContents
simsCol = range("A1")
For x = 2 To 250
If Worksheets("simsData").range(simsCol & x) <> "" Then range("A" & x + 3).Value = Worksheets("simsData").range(simsCol & x)
Next x
simsCol = range("B1")
For x = 2 To 250
If range("A" & x + 3) <> "" Then
If Worksheets("simsData").range(simsCol & x) = range("B2") Or Worksheets("simsData").range(simsCol & x) = range("B3") Then
range(simsCol & x + 3) = "Y"
Else
range(simsCol & x + 3) = "N"
End If
End If
Next x
Dim simsArray As Variant
Dim mapArray As Variant
simsArray = Array("C1", "D1", "G1")
mapArray = Array("C", "D", "G")
For y = 0 To UBound(simsArray)
simsCol = range(simsArray(y))
mapCol = mapArray(y)
For x = 2 To 250
If range("A" & x + 3) <> "" Then
If Worksheets("simsData").range(simsCol & x) = "Y" Then
range(mapCol & x + 3) = "Y"
Else
range(mapCol & x + 3) = "N"
End If
End If
Next x
Next y
simsArray = Array("E1", "F1", "H1", "I1", "J1", "K1", "L1", "M1", "N1", "O1", "P1", "Q1")
mapArray = Array("E", "F", "H", "I", "J", "K", "L", "M", "N", "O", "P", "Q")
For y = 0 To UBound(simsArray)
simsCol = range(simsArray(y))
mapCol = mapArray(y)
For x = 2 To 250
If range("A" & x + 3) <> "" Then
range(mapCol & x + 3) = Worksheets("simsData").range(simsCol & x)
End If
Next x
Next y
Dim realColumn As String
Dim valueColumn As String
Dim columnNumber As Long
Dim realCell As String
Dim valueCell As String
Dim subjectJump As Integer
realColumn = "S"
subjectJump = 8 - Worksheets("menu").range("F17")
For y = 1 To 48
If Worksheets("menu").range("F19") = "Y" Then
valueColumn = range(realColumn & 1)
realCell = realColumn & 1
realColumn = Split(Cells(1, range(realCell).Column + 1).Address, "$")(1)
range(realColumn & 1) = valueColumn
For x = 1 To Worksheets("menu").range("F17")
valueCell = range(realColumn & 1) & 1
If range(realColumn & 1) <> "" Then valueColumn = Split(Cells(1, range(valueCell).Column + 1).Address, "$")(1)
realCell = realColumn & 1
realColumn = Split(Cells(1, range(realCell).Column + 1).Address, "$")(1)
range(realColumn & 1) = valueColumn
Next x
Else
If range(realColumn & 1) = "" Then
realCell = realColumn & 1
realColumn = Split(Cells(1, range(realCell).Column + 8).Address, "$")(1)
Else
For x = 1 To Worksheets("menu").range("F17")
valueCell = range(realColumn & 1) & 1
valueColumn = Split(Cells(1, range(valueCell).Column + 1).Address, "$")(1)
realCell = realColumn & 1
realColumn = Split(Cells(1, range(realCell).Column + 1).Address, "$")(1)
range(realColumn & 1) = valueColumn
Next x
realCell = realColumn & 1
realColumn = Split(Cells(1, range(realCell).Column + subjectJump).Address, "$")(1)
End If
End If
Next y
realColumn = "S"
For y = 1 To 384
simsCol = range(realColumn & 1)
mapCol = realColumn
If range(mapCol & 1) <> "" Then
If range("A" & 4) <> "" Then
range(mapCol & 4) = Worksheets("simsData").range(simsCol & 1)
End If
End If
realColumn = Split(Cells(1, range(realColumn & 1).Column + 1).Address, "$")(1)
Next y
realColumn = "S"
For y = 1 To 384
simsCol = range(realColumn & 1)
mapCol = realColumn
If range(mapCol & 1) <> "" Then
For x = 2 To 250
**If range("A" & x + 3) <> "" Then
range(mapCol & x + 3) = Left(Worksheets("simsData").range(simsCol & x), 1)
End If**
Next x
End If
realColumn = Split(Cells(1, range(realColumn & 1).Column + 1).Address, "$")(1)
If y = 384 Then loopCheck = False
Next y
For x = 5 To 253
If range("A" & x) <> "" Then studentNumber = x
Next x
End Sub