Weird IIS/ASP.NET problem

[LRSFC_DanJ]

We have a web application which is running on IIS 8.5 and ASP.NET 4.6.1 which has for the last couple of months been falling over roughly every 2 weeks.

 

When it falls over:

• iisreset doesn't clear the issue
  
• recycling the application pool doesn't clear the issue
  
• restarting the whole server DOES clear the issue, but only for another 2 weeks
  

 

I'm no developer (I'm in the IT Services department and I've been asked to look at this) but having looked at what's happened, it seems like the code is having trouble handling invalid/expired session states. However, from what I've read, if that was the case then recycling the application pool should have cleared the sessions, as it's configured to store them in-process.

 

Can anyone give me any ideas as to what might be wrong?