memory mapped files disappear randomly - vb.net

Question

I have a camera management system with the following components in vb.net
This has worked well for several years, but is now randomly failing in different programs with a 'file not found' error when accessing the memory file or simply freezing. This occurred after I added a new memory file (GPS2Memory) The design of the system is to have several data readers assembling data from a their own data streams and overwriting the prior values , while 3 control applications read these records and control servos. These actions are asynchronous.
I have tried deleting the MMF.Dispose but the apps continue to fail.
CreateMemoryFiles - Creates 5 memory files (Switch_Memory, INS_Memory, GPS_Memory, AHRS_Memory, GPS2Memory) each is 400 bytes except Switch - which is 20.
ReadAHRS reads a data stream on a com port, and places a formatted csv string in AHRSMemory about every 50 ms.
ReadSecondGPS reads a data stream on a com port and places a formatted csv string in GPS2Memory about every 30 ms.
ReadIMUData reads a data stream on a com port and places a formatted csv string in IMU_Memory about every 30 ms.
ReadSwitch reads a switch status on a USB port and places a formatted csv string in SwitchMemory about every 50 ms.
BankCompensator reads IMU_Memory (for roll data), and SwitchMemory (On or Off) to start servo control.
CameraControl reads GPS2Memory (for WAAS data) IMUMemory (for pitch, roll and heading) and SwitchMemory for starting an stopping servos and shutter events.
I have run all programs in Debug mode :
ReadSecondGPS failed after 16843 cycles - Failed on 'Openexisting" statement with 'Unable to find specified file.
ReadAHRS failed after 12652 cycles, with same error and message
ReadIMUData failed after 45331 cycles with same message
CreateMemoryFiles was still running and when I set a breakpoint, it was at 3679 cycles (Incrementing every 1000 ms) and continued.
I have tested the string length written to the files, and the longest is 109 characters - I set the length longer as the strings get more data as new data becomes available.
Why would Windows lose track of 3 memory files when the initiator was still active?
Here is the create code - this is an endless loop so the memory files should not disappear.
Option Explicit On
Option Strict On
Imports System
Imports System.Net
Imports System.Text
Imports System.IO
Imports System.IO.MemoryMappedFiles
Imports System.Timers
Imports System.Threading
Public Class Form1
Public WithEvents MEMSTimer As New System.Windows.Forms.Timer()
Dim LoopForever As Boolean = True
ReadOnly GPSINS_Memory_File_Name As String = "GPSINSMemoryData"
ReadOnly GPS2_Memory_File_Name As String = "GPRMCmemoryData"
ReadOnly AHRS_Memory_File_Name As String = "AHRSMemoryData"
ReadOnly Switch_Memory_File_Name As String = "SwitchMemoryData"
Dim CycleCount As Integer = 1
Public Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
Dim GPS2 = MemoryMappedFile.CreateNew(GPS2_Memory_File_Name, 20, MemoryMappedFileAccess.ReadWrite)
Dim MMS = MemoryMappedFile.CreateNew(Switch_Memory_File_Name, 400, MemoryMappedFileAccess.ReadWrite)
Dim GPS = MemoryMappedFile.CreateNew(GPSINS_Memory_File_Name, 400, MemoryMappedFileAccess.ReadWrite)
Dim AHRS = MemoryMappedFile.CreateNew(AHRS_Memory_File_Name, 400, MemoryMappedFileAccess.ReadWrite)
CycleCountOut.Text = CType(CycleCount, String)
Do Until LoopForever = False
CycleCount += 1
CycleCountOut.Clear()
CycleCountOut.Text = CType(CycleCount, String)
Thread.Sleep(1000)
Loop
Application.Exit()
End Sub
Public Sub Button2_Click(sender As Object, e As EventArgs) Handles Button2.Click
LoopForever = False
Application.Exit()
End Sub
Private Sub CycleCountOut_TextChanged(sender As Object, e As EventArgs) Handles CycleCountOut.TextChanged
End Sub
End Class
Here is a typical Write code
Sub WriteAHRS_To_Memory()
Dim MMF = MemoryMappedFile.OpenExisting(AHRS_Memory_File_Name)
Dim Bytes As Byte()
Bytes = StrToByteArray(AHRS_Data_Out)
Try
Using writer = MMF.CreateViewAccessor(0, Bytes.Length)
writer.WriteArray(Of Byte)(0, Bytes, 0, Bytes.Length)
' writer.Dispose()
End Using
Catch ex As Exception
MsgBox("mem write error = " & ex.ToString)
End Try
stop_time = Now
AHRS_elapsed_time = stop_time.Subtract(start_time)
AHRS_Update_Time.Clear()
AHRS_Update_Time.AppendText(AHRS_elapsed_time.TotalSeconds.ToString("0.000000"))
start_time = Now
MMF.Dispose()
End Sub
And typical Read code
Sub GetIMUData()
Dim MMS = MemoryMappedFile.OpenExisting(Switch_Memory_File_Name)
Using Switchreader = MMS.CreateViewAccessor(0, 20, MemoryMappedFileAccess.Read)
Dim SwitchByteString = New Byte(20) {}
Switchreader.ReadArray(Of Byte)(0, SwitchByteString, 0, SwitchByteString.Length)
outMessage = Convert.ToString(SwitchByteString)
teststring = ""
teststring = BitConverter.ToString(SwitchByteString)
For i As Integer = 0 To SwitchByteString.Length - 1
SwitchdataIn = System.Text.Encoding.ASCII.GetString(SwitchByteString)
Next
End Using
Dim SwitchString() As String
SwitchString = Split(SwitchdataIn, ",")
SwitchdataIn = SwitchString(0)
SwitchPositionDisplay.Clear()
SwitchPositionDisplay.Text = SwitchdataIn
MMS.Dispose()