There may be a clocking issue with the MixerDelay plugin.
With numerous test it seems the delay to be the correct delay while in 48k but when I clock to 96k the delay is half the shown value.
I found this issue while time delaying my 7.1.4 speaker system. I am recording impulse peaks and then comparing them with each other to ensure my speakers are aligned (and not just using my time delay calculations as true).
That is when I saw the 96k test show up shorter than they should be.
I did notice that the StereoDelay plugin works fine in all sample frequencies.
The MixerDelay is a great plugin and I am thankful it was created as it simplifies management and routing.
Hope this helps.
I did reboot my PC and and RME.
RME UFX USB.