JmDNS has changed in its semantics WRT case-sensitivity which breaks ECF
discovery. You can see the effects, if you run the ECF discovery tests
on the JmDNS 3.x branch.
Is your final conclusion that the 3.4.x version is not capable to handle our discovery? I would really hate to spend a lot of time just retracing your steps. JmDNS seems abandoned. So upgrading to a defunct 3.4.1 is not "bringing us op to date".
Instead we might consider dropping JmDNS and go for another library.