Hey all, wanted to post this before the thread goes too cold - and for anyone that comes across it in the future.
A little more poking around with the PDO part of the shader and I found the specific node that is causing the blacked out foliage instances. “ObjectScale” cannot be used with Foliage Instances, and you need to use FoliageScaleFactor instead. It will slightly break your handplaced foliage, but setting your PDO value to something like 1.5 or 2 (instead of 1 by default) works pretty well.
Hopefully this fix works as well for ya’ll as it does for me. 
(All the distant trees here are Instanced Foliage WITH PDO hooked up and working)