Why first pocess calls, after app pool recycle, are failing?

Question

PROBLEM: In a Sharpoint + BPM solution, running Windows 2012 with IIS 8, after the application pool is recycled, the first call of any type of process fails, all subsequent calls are successful.

Starting from an ascx embedded on an Sharpoint solution, one ascx per process type, we click a button that originates a server.transfer to a new page that creates a new instance of the pretended process type, if this suceeds, from here we response.redirect, with query string rewrite, to the new process instance just created. In the case of error (1st process after recycling) this last step does not ocurr.

As the page that instantiates de process is dynamic, depending on the type of process choosed, it could not be pré-loaded before start the solution, if we force the pré-instantiation of these pages at start-up, we could end up with a dummy process, one of each kind, at every new application pool recycle (once a day).

QUESTION: How can I locate [MyApp].XMLSerializers.dll and unload it in order to validate my theory that it’s absence is responsible for the 1st processes call failure?

SOLUTIONS ATTEMPTED:

• Optimization of the Application Pool and Site configuration
  No Results
• Search for DLL bind errors
  Using FUSLOGVW, after recycling application pool it seems that, in a first try, the [myApp].XMLSerializers.DLL, among others, is missing. As this is a time consuming step and the error does not happen when tracing (even only for event viewer) is enabled I supose that the on the fly generation of the DLL with all serializable types could be related to this issue.

Findings:

• Afects also processes that don’t consume web services
• When trace is on there is no error
• Afects all environments

Any advice greatly appreciated
Many thanks, LTS