Go to the XcomGame INT File located here:

XCOM 2\XCom2-WarOfTheChosen\XComGame\Localization\INT

Search for "Items!" here. Put the weapon or item with the error right beneath this for simplicity with all the other ones in the game.

Copy and paste the following with whatever weapon or item you want replacing this example:

[VektorRifle_CV X2WeaponTemplate]
FriendlyName="Vektor Rifle"
FriendlyNamePlural="Vektor Rifles"

As long as you have the template name for your item, you can add it here. You can use the other items in this file for reference on proper formatting.