Yeah, I have nine flash grenades, but no option to return any
Flash Grenade x9 [Equip][Send][Sell][Trash]
Checking the faction armory, I see an option to retrieve the flash grenade that I do have loaned out, and have now done so.
Perhaps, in the faction armory, it would be prudent to give members the ability to see all the items a particular member has loaned out? Also I presume a "Return" option should be next to the flash grenade
After retrieving that flash grenade, I was able to leave the faction.