We control all of our measurement equipment w/ SW. For only the E8257D synthesizers we have a random problem come up.
At a random interval, we will lose TCP connection to the device (seems like the instrument is just dropping the TCP connection). It happens to random synthesizers at random times. This is mostly a recent occurrence (no recent firmware upgrades). The synthesizer is at firmware C.05.37.
We did have this issue a while ago but we set the keep alive timeout to 75 seconds using setsockopt (from the default 60 mins) and that seemed to clear the issue until recently.
Restarting the SW clears the issue up (at least temporarily).