ASP.NET & SQL Server 2012 timeouts once a month
It might be related with leaking connections exhausting the connection pool.
If the connections are not released properly they will remain active and will not be returned to the connection pool until the next Garbage Collection executes. If a lot of connections are opened in a short time the connection pool might fill up before the GC runs, and the following connection requests will end up waiting for a free connection in the pool, eventually timing out.

https://msdn.microsoft.com/en-us/library/8xx3tyca(v=vs.110).aspx