Okay, after playing a bit more I have found that this skill kinda works (still bugged though), but the game is SUPER confused with the chaos lord of khorne in general as to whether the units targeted by "Unflinching Soldiers" (US) should be shown as having the 10% physical resistance or not on the campaign map.
In my campaign, after I achieved the long victory for the +10 lord recruit rank, I recruited another chaos lord at rank 13 and this time the chaos warriors and other units were shown as having the 10% physical resistance BEFORE I unlocked US. On top of that, this was only shown in the local recruitment section, NOT global recruitment (10%phys res local, no phys res global). After that I put the skill point into US and the unit card attributes remained exactly the same in both local and global recruitment for the unit cards' previews. After the end turn, however, the unit card preview showed correct stats for both local and global recruitment (10%phys res local, 10%phys res global). And finally for reference, when I made the original post the stats showed as (no phys res local, no phys res global). Additional FYI; I reload or exit the game during my campaigns pretty often, and that didn't seem to do anything at all.
The Chaos Lord of Khorne's skill "Unflinching Soldiers" doesn't do anything right now. I checked for regular chaos warriors of Khorne and regular chaos knights of Khorne.
The chaos lord of khorne and Daemon prince of Khorne don't have any basic army buff skill (only rank 7+ skill) for the ror marauder berserkers (Brutes of the Hound), they should be included in the "Chaos Vanguard" skill. The other lord types do buff them.
Finally there is no basic army buff skills (only rank 7+ skill) for ANY of the Khorne lords that buffs the Ghorgon ror (The Bloodbrute Behemoth). It should be included in the "Monstrous Strength" skill for the Chaos lord of Khorne and Daemon Prince of Khorne, and the "Harbingers of Death" skill for everything else.