Same problem with a 2xslave setup cubase 9 host.
i7-6770k 64gb ram win7 host - RME raydat (radar24-clocked) 256buffer - cubase 9 (latest) - vep6, 16+kontakt, ew play, spire, serum, sylenth, uvi wrkstation, omnisphere, keyscape
i7-2600k 16gb ram win7 slave1 - vep6 - same software
i7-2600k 16gb ram win7 slave2 - vep6 - same software
Gigabit through hardwired switch and static ip. cat6 cable I crimped myself.
Literally the same issue... the audio engine is just blank after an extended period of time. it's never quit during use, just after returning from a 24 hour period+ of not being used. Midi appears to be functioning but no audio seems to be coming back through the ASIO lanes.
Paul, if you want to track this down even further, let me know what you would need. I have a background in software development so i'd be open to helping you nail this one down. Definitely not a sleep or hibernation issue on my end. What else could possibly cause a timeout issue?
Also, I have not taken the time to roll back to 5 or 4 and wait for the problem fyi. Next time I get the issue, I'll see if there is ANY way outside of close and reload that can fix the issue. might help in tracking down the source.