I found a similar case? in thread #160096? (May2019)? same errors. The thread is a dead end or so.
Paul Bender worked the issue and it might have been partially resolved in a JMRI test build 4.15.8.? You might try and download that test release and see if it works for you.
Paul still works on Hornby Elite and ExpressNet? as per GITHUB. His last? add was in 4.16 for the Elite programming. Something might have been broken afterwards in your 4.17.6
If not done, you might update the firmware on your Elite to 1.44
https://www.hornby.com/uk-en/hornby-dcc/elite-firmware-update.
Other thought is get on GITHUB JMRI and tell them your problem.? You might help them out.
Marc
