Wrap context creation in transaction.

lib/pleroma/web/twitter_api/twitter_api.ex

@@ -319,6 +319,7 @@ defp make_date do
   end
 
   def context_to_conversation_id(context) do
+    {:ok, id} = Repo.transaction(fn ->
       with %Object{id: id} <- Object.get_by_ap_id(context) do
         id
       else _e ->
@@ -326,6 +327,8 @@ def context_to_conversation_id(context) do
         {:ok, %{id: id}} = Repo.insert(changeset)
         id
       end
+    end)
+    id
   end
 
   def conversation_id_to_context(id) do