For some odd reason the other parts of the SSRA with Donal's armor have no issues but when trying to place the Plate SSRA Ornamentation into the Plate arms (Donal's Vambraces) unable to do so as if it was not plate.
Check and see if the armor gives a plate visual when equipped. The PoP plate helms are classified as cloth for some reason and don’t have a graphic. As Febb said, this is likely the problem.
heads don't have a helm graphic. I think it is the latest fashion at the time. Although it was not a problem at the time, as the times advanced, the preference changed and it was regarded as a problem.
This is likely a bug. The ITEM_CLASS for Donal's Vambraces is Miscellaneous instead of Armor. Will look into addressing this for the July update. Thanks for letting us know!