You may be using the current client config object to retrieve the current user’s object id. And that used to work just fine.

object_id =  data.azurerm_client_config.current.object_id
However, for me, this started returning an empty string. This was the workaround I found:
#AV - diff route to get current user object id

data external account_info {
  program                      = [
                                 "az",
                                 "ad",
                                 "signed-in-user",
                                 "show",
                                 "--query",
                                 "{object_id:id}",
                                 "-o",
                                 "json",
                                 ]
}
/*output user_object_id {
    value = data.external.account_info.result.object_id
}*/
Summary
data.azurerm_client_config.current.object_id  does not return a correct user object id can be fixed by using a different approach – shown above.