w3wp.exe fails and web restarts every ~75 seconds

We have a farm of 5 Windows Server 2012 R2 servers, running IIS.

Under load, one website start failing every ~75 seconds and it keeps going on and on, until load goes down at night time.

Only thing we have to go after, is the message in the evenlog :

Faulting application name: w3wp.exe, version: 8.5.9600.16384, time stamp: 0x5215df96
Faulting module name: clr.dll, version: 4.0.30319.34209, time stamp: 0x5348a1ef
Exception code: 0xc00000fd
Fault offset: 0x000000000001ff16
Faulting process id: 0x73d0
Faulting application start time: 0x01d31e49290c950a
Faulting application path: c:\windows\system32\inetsrv\w3wp.exe
Faulting module path: C:\Windows\Microsoft.NET\Framework64\v4.0.30319\clr.dll
Report Id: 8a491461-8a3c-11e7-80e8-d89d6731bc04
Faulting package full name: 
Faulting package-relative application ID: 

If I look at the "Workers" inside IIS, I just see a bunch of requests and the wait time keeps going up and up when I press F5 - until the process is crashing/restarted.

Any advise ?

The application is written in C#/VB, and uses controls from Telerik, saves data inside a Sql Server and caches via a distributed nCache running on 5 servers.

The application has been running for months without updates, other that patches to the OS regularly.