For now, I have triggered a manual invocation with "run now" to see if that temporarily resolves the problem, but I would like to know why scheduling did not perform as documented in the first place.

It's sleeping, please do not use app sleeping with crons.

I see, is there a reason the option is even available for crons? Can it be removed? (Or documented at least?)

You're right, there's no reason it should be shown when you have a cron expression set.

Can you help me to understand what you hoped to achieve my enabling it on a CRON service?

I don't recall enabling it at all. This service used to be an "application-style" cron job where the timing logic was implemented in my application code, as was formerly recommended in the Railway docs. I converted it from that to the newer cron style, but the service never took any user requests and has never had any domains associated with it.

Did this option get enabled by default when you added the feature?

We would not have enabled this feature for you.

Even with an in-code cron scheduler you would also not want to use app sleeping.

So would I be correct to assume you had accidentally enabled that at some point?

It's definitely a possibility that I enabled it mistakenly when turning on the setting for some of my other applications that actually do serve user requests, and hence are appropriate for app sleeping. Without an audit log, I can't say for sure. But yes, it clearly makes no sense for me to turn it on for any kind of cron job.

Okay then I will mark this as solved!