Asp.Net site hangs

Question

IIS

There was a following problem:

The asp.net site working on IIS hangs up from time to time. The site is running on windows server 2008 R2. The server itself continues to work normally.
Hanging is expressed in the fact that the site simply stops responding.
The problem is exacerbated by the fact that sometimes not the entire site freezes, but only the web service running on it. However, the www service continues to function normally. Sometimes the entire site freezes.

Trying to reload the site (via IIS) does nothing. If you try to stop the pool, it stops but refuses to start (Error message: "The service cannot currently accept commands (Exception from HRESULT: 0x80070425)"). If you transfer the site to another pool, then the site starts immediately. And the pool that gave an error also immediately turns out to be launched.

Since sometimes only a web service crashes, additional ones were added there. logs. After every line. It turned out that the server starts to perform AES decoding (using the standard library), but does not reach the completion of decoding. At the same time, during normal server operation, there are no problems with this.

The site does not produce additional streams.

The site worked some time ago on a different server - there have never been any such failures. Now the problem is reproduced somewhere once a day.

Tell me, please, what could be the problem?