@JColvin Thanks for the extensive answer, but @attila hit the point: It's a bit unexpected, but indeed the transfer time was rather long. If I change from 4Mi to 2Mi samples or reduce the number of inputs from 32 to 16, the repeated mode works again.
I'm looking for events happening seldomly, so the data transfer time doesn't matter in this case. Maybe one can replace the full stop by a short sleep between end of transmission and going to armed mode again? Then there should be enough time for the application to respond to user action, but it also eventually returns to data taking.
Thank you!