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.   re:   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