Dropbear ssh server immediately quits after startup

I built a linux kernel (v. 5.17.1) with default config and created a minimal root fs using buildroot (both for x86_64). I modified the configuration of buildroot to use glibc and added DHCP for eth0. Furthermore I added a dropbear ssh server. I can boot into the system using qemu:

qemu-system-x86_64 -m 1G -kernel linux-5.17.1/arch/x86_64/boot/bzImage -initrd buildroot-2022.02/output/images/rootfs.cpio -net nic -net user,hostfwd=tcp::2222-:22

The logs state that dropbear (sshd) is started successfully, however the server is not running when trying to connect. I can start it manually using /etc/init.d/S50dropbear start, which also states that it was successful. But it seems to quit right after it started. If I run dropbear in the *do-not-fork* mode in the foreground, everything is working fine, i. e:

dropbear -FBR

Does anyone have an idea why this could be the case?