I’d suggest first verifying that your iscsi target is also running on system(s) that are fully updated and perhaps even running a version that is close to what you’re running in Tumbleweed.
I also don’t personally track what versions are running in Tumbleweed, since you’re already testing in a virtual machine, I’d recommend you also test in a LEAP machine.
You should submit a bug with your detailed findings to https://bugzilla.opensuse.org
The error suggests a coding error and not something a User would be expected to be able to address.
TSU