portserver TS8 all ports stopped working

We’ve been using a Portserver TS8 for years to control serial interfaces between a PC and other vendors’ systems.
We are using 7 or the 8 ports. All 7 stopped communicating at the same time the other night.
We can still access the web portal of the Portserver. We can ping it.
On the PC, the ports show that they have been acquired.
But no data flows.
What would stop traffic from flowing from the Portserver to the PC?
The pc is Win 7, recently updated with May security updates.

We tried another PC - a Win 10, same result.
The pc application that communicates over the serial ports does not show a connection error (as it normally would if there were a bad connection), just that it is not receiving data.