When waking up after one hour third monitor does not turn on
 

I have a Mac Mini late 2012, 16 GB RAM, El Capitan and 3 Samsung 24" monitors.

Latest Displaylink driver is used.

Everything is working fine, no problems so far with any app.

When I return to work and log in, the Displaklink attached third monitor does not wake up from standby and the only way to use it again is unplugging and plugging the USB 3 connector.

Now I use an external powered USB 3 hub with the same problem so it has nothing to do with the mini USB 3 ports powered off when the Mac is locked.

Any ideas why