https://github.com/ros-planning/navigation2/blob/c6294747a59e41e51d6d833c9b6fe93123f78b8b/nav2_behavior_tree/include/nav2_behavior_tree/bt_action_node.hpp#L100

The exception message that is being printed in case an action server is not up by 1s is "Original error: basic_string::_M_create", whereas it should be Action server <action server name> not available"
One of the ways to fix it, in case it reproduces not only for me, is by replacing the above with

    std::runtime_error(std::string("Action server ") +  action_name + std::string(" not available"));