C-Block DLL never invoked — QSpice's own auto-compile silently fails, but manual dmc.exe compile succeeds every time

QSPICE
2

Download these two files and check if you can execute them.
From your description, it seems that the reason your simulation cannot run is related to an incomplete circuit (a floating node where something is not connected), rather than a DLL issue.
dll_test.qsch (1.4 KB) | dllex.cpp (1.4 KB)
dll

Review this post to increase your trust level in forum to upload your schematic and .cpp for review.
Qspice Forum - New User to Basic User (File Upload) - QSPICE - Qorvo Tech Forum

Here is a tutorial working with DLL from scratch.
Beginner Tutorial for QSpice (Community Sharing) - QSPICE - Qorvo Tech Forum