As a test, I would disable write-back cache and see if it makes any difference. Your overall latency may be higher, but maybe there's something in that controller's microcode that is generating this.
Thanks for the reply. We didn't try changing the writeback policy.
Changing firmware and driver versions in the 2019 time frame didn't seem to make any difference.
Astoundingly, the solution was to downgrade the firmware of the iDRAC on our server to a version from December 2018. Apparently, the iDRAC controller polls the storage controller on a schedule and that was causing the datastore disconnections.
Dell supposedly will have an updated iDRAC firmware out in December 2019 that should fix this issue.