.FindNext in a loop doesnt' work - excel

Question

I am using this loop to look for values. .Find works but findNext does not, ommiting many values. Here I drop my code, do you have any advice? thank you very much!!
For Each ws In SourceWb.Worksheets
If IsNumeric(Left(ws.Name, 3)) Then
Set gCell = ws.Columns(6).Find(what:=numdoc, LookIn:=xlValues, lookat:=xlWhole, SearchOrder:=xlByRows, MatchCase:=False, searchformat:=False)
If Not gCell Is Nothing And IsNumeric(Left(gCell.Parent.Name, 3)) Then
firstAddress = gCell.Address
Do
repetidos = repetidos + 1
finalcell = gCell.Address
'merged cells code here not displayed
oldaddress = gCell.Address
'>Having trouble here> **
Set gCell = ws.Columns(6).FindNext(after:=gCell)
'**
Loop Until gCell.Address = oldaddress
End If
End If
Next ws

Answer 1

This was the best I could derive from your clues:
Option Explicit
Sub Test()
Dim WS As Worksheet
Dim SourceWB As Workbook
Dim numdoc As Long
Dim gCell As Range
Dim firstAddress As String
Dim oldaddress As String
Dim finalcell As String
Dim repetidos As Long
Set SourceWB = ThisWorkbook 'added for clarity and safety
numdoc = 456
For Each WS In SourceWB.Worksheets
If IsNumeric(Left(WS.Name, 3)) Then 'OK I had to save it as "123 A"
Set gCell = WS.Columns(6).Find(what:=numdoc, _
LookIn:=xlValues, _
lookat:=xlWhole, _
SearchOrder:=xlByRows, _
MatchCase:=False, _
searchformat:=False)
If Not gCell Is Nothing And IsNumeric(Left(gCell.Parent.Name, 3)) Then
firstAddress = gCell.Address
Set gCell = WS.Columns(6).FindNext(after:=gCell)
Do
repetidos = repetidos + 1
finalcell = gCell.Address
'merged cells code here not displayed
oldaddress = gCell.Address
Loop Until gCell.Address = oldaddress
End If
End If
Next WS
End Sub
Not sure if it answers the question but, it does demonstrate indentation.
There's probably room for a With...End With in there but I'm too tired to look for it.

Answer 2

This seems to work at this point.
For Each WS In SourceWB.Worksheets
With ws.Range("F:F")
If IsNumeric(Left(WS.Name, 3)) Then 'OK I had to save it as "123 A"
Set gCell = .Find(what:=numdoc, _
LookIn:=xlValues, _
lookat:=xlWhole, _
SearchOrder:=xlByRows, _
MatchCase:=False, _
searchformat:=False)
If Not gCell Is Nothing And IsNumeric(Left(gCell.Parent.Name, 3)) Then
firstAddress = gCell.Address
Set gCell = .FindNext(after:=gCell)
Do
'merged cells code here not displayed
Loop While Not gCell Is Nothing And gCell.Address <> firstAddress
End If
End If
end with
Next WS