Do you bought the two D3 as new from Bitmain or in used condition?

Maybe ASICS are burned out, see the lot of HW errors, they will mostly never be come back. Use the tip from blissz - when this not helps you have a problem.
S9 / L3+ have stable ASIC's but the ASIC's from D3 burning out very easy, simply a longer time chip temp above 75 or 80 degrees kill them
and IMHO the frequenzy and voltage set from Bitmain on the 19 GH/s batch is to high for a long time 24/7 ASIC runtime.

When i read the "overclock" posts here - simply do it and you will kill all your ASIC's after a week or so.
This is good for decreasing the DASH difficulty...