Wyse 3040 Dual Monitor no Signal after sleepmode

Hello at all

we have the following problem with Wyse 3040 and ThinOS 8.6_412 and several monitor models/vendors.
Sometimes after the ThinClient puts the connected Monitors into sleep mode, one monitor or both stops working. 
No Signal from Wyse 3040 till the resolution is changed manually or the ThinClient was rebooted.
This occures only when two Monitors are attached to the Wyse 3040. 
We notice this  behavior allready with older version of ThinOS, perhaps 8.6_27, we don't know the exact version.
Both monitors are connected via DisplayPort cable without any adapters. 
Monitor-Resolution depends on the attaced Monitor via DDC, and there is no rotation configured.
Problem occures till now with Philips Monitors (Resolution 1920x1080) and iiyama Resolution (2560x1440)
Does anybody notice the same Problem?

Many Thanks
Best Regards
Gopher-01