SSL issues: SocketException: Socket already closed

Hello

for some days we are observing strange errors on our PI systems related to ssl communication failing. For example

Failure at Cache-Refresh data consumption !!!
<?xml version="1.0" encoding="UTF-8"?>
<CacheRefreshError>
  <EngineType>AE</EngineType>
  <EngineName>xx.xxx.xxxxxx</EngineName>
  <RefreshMode>C</RefreshMode>
  <GlobalError>
    <Message>
      Couldn't parse Configuration Data cache update XML string from Directory.
    </Message>
    <Trace>
      java.net.SocketException: Socket already closed.
at iaik.security.ssl.SSLTransport.a(Unknown Source)
at iaik.security.ssl.k.available(Unknown Source)
at java.io.BufferedInputStream.read(BufferedInputStream.java:325)
at com.sap.engine.httpdsrclient.io.ServerInputStreamWrapper.read(ServerInputStreamWrapper.java:49)
[...]

    </Trace>
  </GlobalError>
</CacheRefreshError>

We always get "java.net.SocketException: Socket already closed" also in other situations like sld registration. The error occurs both on a 7.11, 7.31 and 7.4 system. All certificates seem to be ok. On one system we even have it when opening a PI directory object:

I did not find anything helpful in the net. I also have opened a ticket at SAP but gid not get a reply yet.

Any hint will be appreciated.

Regards, Jochen