I am having the same issue as
I have a couple of Draytek routers (different models than the other post, but the same MIBs apparently) that lost the VDSL line speed after a f/w update. Draytek have moved the speed OIDs out to the VDSL MIB. The consensus of that post was that LibreNMS needed a bit a of feature add to support the 251 VDSL MIB. And PipoCanaja had a 3rd party device support issue that was hindering development. That post has closed. I was wondering if any progress has been made. I’d be happy to help with any testing if that were possible.