Monitor won’t awake anymore z90dw

Hello,
We have some z90dw clients with hp la2405wg monitors connected to it.
Somtimes not always this monitor goes into sleep mode and won’t wake up until we disconnected and then reconnect the dvi or displayport cable. This behavior doesn’t show with the hp lp2465 monitors. On the monitor we disabled all the powersaving options we can find. On xpe the powersetting is off after 15 min. It happend when the client is also still on the wyse desktop.

Does someone recognize this problem ?
thanks in advance.
Hank van Asperen