I am experiencing the same issue with a brand new build (GA-H170N-WIFI) and Opnsense. Tried img/iso and multiple USB. Updated BIOS on board. Nothing works.
Just a sanity check - sam USB stick, pfSense latest IMG, Rufus DD write works fine and boots.
Just a sanity check - sam USB stick, pfSense latest IMG, Rufus DD write works fine and boots.