ASP MVC Applicaiton hangs suddenly in IIS 8.5

We have 3 Servers One is for infrastructure like domain server and 2 servers with an ASP MVC and a webapi site. A maanged load balancer balances the load to server 2 and 3

For many monthes everything works fine, but since the last weeks we notice ocassionally hangs of server 2 and 3 most of the exceptions in the eventlog are:

Exception information: Exception type: HttpException Exception message: The remote host closed the connection. The error code is 0x80070057. at System.Web.Hosting.IIS7WorkerRequest.RaiseCommunicationError(Int32 result, Boolean throwOnDisconnect) at System.Web.WebSocketPipeline.DoFlush() --- End of stack trace from previous location where exception was thrown --- at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw() at System.Web.WebSocketPipeline.d__8.MoveNext()

Some times the error code varies and is 0x800704CD . In this state the cpu usage increases up to 99,5% on the w3wp processes. Network and RAm Usage is very low

Also sometimes in this szenario we can see a hughe amount of authentications inthe security log. Its the user with which the site is running.

This error doesn't occur on peaks. Two times we had it in the night where we had nearly zero traffic.

When i look in the Worker Processes UI i can see there are many (30+) Connections in the EndRequest state. is this expected to be ? Thats more then we have as concurrent users at this point in time

We didn't change installation on the servers the traffic only increased slightly.

Any advice is very welcome.

Are there any further informations that could be important?