I found out why Templar's forearm is invisible.
The setting name of property in XComGameData.ini is not vaild one.
U can fix it by replace the text to below.

..\2893908268\Config\XComGameData.ini
The 9th line:

From:
+Loadouts=(LoadoutName="SquaddieTemplar", Items[0]=(Item="TemplarArmor"), Items[1]=(Item="Sword_CV"), Items[2]=(Item="BallisticShield_CV"), Items[3]=(Item="FlashbangGrenade"))

To:
+Loadouts=(LoadoutName="SquaddieTemplar", Items[0]=(Item="TemplarArmor"), Items[1]=(Item="ShardGauntlet_CV"), Items[2]=(Item="BallisticShield_CV"), Items[3]=(Item="FlashbangGrenade"))

Solution and report found by Ralbbino