Hi, my dmp files are also dummy files of 1kb, but in my case I am mainly interested in callstack generation which happens anyway and is uploaded to my crash report server (I use BugSplat).
Can you try these 2 different options?
apt-get install -y systemd-coredump
ulimit -c unlimited
Possibly the coredumps are saved here: /var/lib/systemd/coredump
Please let us know if/how you get it working because minidmp would be useful!