Trains without schedule in automatic mode have a state of no_path instead of no_schedule. Additionally, they switch to path_lost and back to no_schedule every 128 ticks (identical to #69772).
You can use the same save and procedure as in my report #69772. Just remove the only entry from the train's schedule and register for the event as described there.
[kovarex] [0.17.43] Train without schedule is in path_lost/no_path state
Re: [kovarex] [0.17.43] Train without schedule is in path_lost/no_path state
Ok, fixed for another release.