Hi,
In the past couple of versions of VE Pro 5 I am experiencing a similar issue. After a period of inactivity Cubase will generate midi, the activity light will flash on the VE Pro plug-in but no midi is received at the server end. I am using 1 instance locally and no EW products are included anywhere in the set-up. I have a fixed IP address.
If I attempt to play an instrument in Kontakt using mouse and keyboard no sounds are generated (as if the server is not connected). The server interface shows the 'slave' to be connected - the server instance shows as connected to localhost as does the instance and the instance GUI is responsive - just doesn't receive midi or instruments make sound. Both Cubase and VE Pro are capable of saving.
After that, the symptoms are the same - any attempt to switch engine off and on and so forth will cause both Cubase and VE Pro to crash. If I attempt to disconnect, Cubase will crash. If I hard quit Cubase and re-open the project file, force disconnect the VE Pro server in order to reconnect, both Cubase and VE Pro will crash on attempted reconnection.
The only solution seems to be to force-quit both and re-open the project from scratch. As there have been a couple of updates to Cubase during the same period and I have added new plug-ins there could be a number of causes - but VE Pro is where the symptoms are produced.