Issues caused by frequent application restarts are pretty common. If you are interested in what causes application restarts in general, and how you can monitor application restarts and what causes them you should read this post:
ASP.NET Case Study: Lost session variables and appdomain recycles
The most recent one was one where the ASP.NET site would respond slowly at regular intervals (read: it grinded to a halt every few hours).
First shot at gathering data:
We started off by getting a memory dump with debug diag when the process was responding slowly. Unfortunately at the time that the dump was taken no requests were executing (i.e. ~* e ! ...
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