Postgres Error `(Postgrex.Error) ERROR 57014 (query_canceled) canceling statement due to user request`

There are unique fields in the User table which can cause conflicts. So we introuduced the on_conflict: :nothing.

Repo.insert_all(
  User,
  [
    %{
         user_id:  user.id,
         wallet_source_id: source_id,
         number: "..." 
       },
      %{
         user_id:  user_2.id,
         wallet_source_id: source_2.id,
         number: "..." 
       }
  ],
returning: false,
on_conflict: :nothing
)

Subsequently, no unique constraint errors but we are seeing postgres throwing

** (Postgrex.Error) ERROR 57014 (query_canceled) canceling statement due to user request

Any insights to the possible root cause?