crond does not start an executable on system start

I've edited the connfig with crontab -e, so it looks as follows:

# ...
@reboot /root/app/bin/myexecutable
# ...

the file exists, is executable and i can run it from command-line.

i've checked it looks ok with crontab -l. i started the service with rc-service crond start && rc-update add crond. then i reboot with reboot and after the reboot i can't see it running in ps -a output.

where can i find the logs? any clue?

alpine linux 3.14.2 running in qemu vm.