Hi,
I assume you have the application activated in Arturia Software Center.
I doubt this is about Piano V. As you say, then that work. Look like it could be a connection or USB power issue.
if you get the issue suddenly while you play, then try to use another USB port on your computer and another USB cable.
If you use a USB hub, then be sure it does'nt give power issues.
If it's not about that, then also be sure your computer is'nt set to shut down USB power. Especially if you have the issue after a break, this could be the solution.
That's something to check.