This includes such high profile gods and goddesses as Devera, who blessed the brooms used to sweep temples, Laverna, goddess of charlatans and theives, Lua, who specifically existed to have weapons captured in war sacrificed to her, Picus, an Italian god of woodpeckers, or Salus, goddess of specifically the welfare of people living in the city of Rome.
How much more specific and unknown do you want to get? There are plenty of surviving deities from the Roman era who have no surviving function that we know of.
List of Roman Deities
This includes such high profile gods and goddesses as Devera, who blessed the brooms used to sweep temples, Laverna, goddess of charlatans and theives, Lua, who specifically existed to have weapons captured in war sacrificed to her, Picus, an Italian god of woodpeckers, or Salus, goddess of specifically the welfare of people living in the city of Rome.
How much more specific and unknown do you want to get? There are plenty of surviving deities from the Roman era who have no surviving function that we know of.