Although all data is correct, Subscriptions / Fetch Subscription Updates does nothing

It is the 1st of February (the end of dry January), but the following subscription does not generate an invoice:

Subscription Start Date: 01.01.2024
Current Invoice Start Date: 01.01.2024
Current Invoice End Date: 31.01.2024
Generate Invoice at Beginning of the current subsciption period
Generate New Invoices Past Due Date
Status Active

Since the Scheduler is not used, there is no debug output there. But also the log files contain exactly nothing. The only place to see any reaction on pressing Fetch Subscription Updates is in bench’s console output, though nothing usable there.

How does one debug this?