Hi everybody

I'm using 2 old Multiface-I boxes with 2 pci-e cards, Windows 10, Cubase 9.5
The cards are properly synced via word clock
Here's the problem:
In Cubase, whenever i am adding an input or output bus to the VST connections which is routed to the 2nd Multiface's i/o, immediately the audio output drops and no sound can be heard anymore. Cubase meters still showing signal but TotalMix won't.
Strangely, when i change buffer size sometimes the audio comes back to life. But mostly not. So it seems that the Asio connection Cubase out ->RME is lost
When i cancel this bus i/o routing from the VST Connections-panel the output sound restores and can be heard again. 
In the past this problem occurred  only occasionally but now it's present all the time.

I used to have the exact same problem starting over a year ago with a larger setup of 3 HDSPe Raydats on another windows 10 computer belonging to my partner, I had to try and deal with it as i am more "techie" than he is. His system is now stable except sometimes weird audio latency starts with no relation to the buffer size settings, and i found out that if i'm saving the file project when it happens the problem will maintain when loading the same file again. So the workaround is to quit without saving, and after restart it all goes back to normal.

I have checked i'm using the latest firmware, tried physically changing the pcie card slots, use different sync methods SPDIF/ADAT/Word clock (always confirmed by the SyncCheck tool), using 3 different versions of cubase - 5, 9.5, 10, installing different HDSP driver versions, all to no avail.

Any ideas would be much appreciated.

Thank you

Yaron