Same FlexApp Applications work in one environment and fail in another.

Problem:

There are no applications mounted in the disk manager

Symptoms:

In order to validate in this case if the issue is similar to the expected error, you can review for this in the FlexApp DIA log.

You first want to have debug mode logging on

See: https://support.liquidware.com/hc/en-us/articles/210632023-Where-To-Find-ProfileUnity-Logs

then obtain a diagnostic in debug.

https://support.liquidware.com/hc/en-us/articles/210325586-How-to-Collect-Logs-Using-the-Diagnostic-Tool

Once extracted, under the user logs section you'll see a Main FlexApp DIA log.

The logs could show multiple application playback attempts or failures. The below error will show up in the client log indicating and issue accessing the token file. 

Virtual Disk will not mount, InvalidOperation, The collection has been modified. The inventory operation might not be performed. is shown in the DIA log:

2025-10-11 09:49:08.533 [6] ERROR - write token error 'C:\FADIA-T\VHDW\7e9dd04001e7dfd8842466939087b999\S-1-5-21-2857351402-2812262531-3171228550-2597642.token', error 'IOException' 'The process cannot access the file 'C:\FADIA-T\VHDW\7e9dd04001e7dfd8842466939087b999\S-1-5-21-2857351402-2812262531-3171228550-2597642.token' because it is being used by another process.', skipping

Resolution:

It is possible that the user has the same application assigned in several different places within the configuration. 

Please edit the LwL.ProfileUnity.client.exe.config file. It is a part of the client tools. 
Please set the tow below values from True to False. 
 
 

<setting name="FlexAppNonJitCutReplayInParallel" serializeAs="String">
    <value>False</value>

<setting name="FilterParallelEvaluation" serializeAs="String">
    <value>False</value>
  </setting>

Additional considerations

If you're using a startup GPO that runs LwL.ProfileUnity.Client.Startup.exe from a shared location (typically \\domain\NETLOGON\ProfileUnity), to ensure that your changes to the client tools on the image are not overwritten please follow the below. 

1. Backup the current contents of \\domain\NETLOGON\ProfileUnity.
2. Extract the client-tools.zip 
3. Edit the  LwL.ProfileUnity.client.exe.config file. It might be necessary to save the file outside the zip file and copy/replace once edited. Save/close the zip file. Make sure the zip file contains the changed file. Make sure the folder is zipped client-tools.zip . It should not be left unzipped. Also, the client-tools folder should not be inside the zip folder.  For instance, once extracted it should look like
   1. Client.Net\Files vs Client.Net\Client.Net\Files

4. Reboot or force GPO update (gpupdate /force) on target machines.

   Important: Always backup existing files before replacing them. Validate the .config changes in a test environment before wide deployment. If using both GPO and base image installs, ensure consistency in the config file across both.