9/17/2019 Update: may have got to the bottom of this. Please try 6.7.3-rc3 available on the next branch.
9/18/2019 Update: 6.7.3-rc4 is available to address Very Slow Array Concurrent Performance.
Trying to get to the bottom of this... First we have not been able to reproduce, which is odd because it implies there may be some kind of hardware/driver dependency with this issue. Nevertheless I want to start a series of tests, which I know will be painful for so