well as an example of the kind of problems you can get with standards and odd things that can happen with new trains and the increasingly complicated software used to run them. Remember back last year when the national grid had a power supply wobble, that resulted in blackouts in some places and the frequency of the grid power supply dropped below 49Hz, which for most people didnt cause much of an issue.
But an unknown (or at least its implications were unknown at the time) safety feature of Thameslinks class 700s and 717s was if their power supply dropped below 49Hz, and note Network rails spec standard says the minimum could be 47Hz, the train software put the train into a failure mode which only a manual reset could fix.
Siemens had coded the trains to work from a nominal 50Hz supply and not expected the supply to drop below 49Hz, which fair enough is a rare occurence, but it doesnt follow the full range of NRs spec, and so the trains stopped and refused to go any further, now some of the trains running an earlier software version, allowed the driver to reset and carry on, the others required an engineer with a laptop to reset. and Siemens have been working on a software patch to fix this for the future.
Which makes me think maybe its similar kind of thing happening here and NRs barriers and signalling system on these rural lines is setup to be within the published standard still, but the tolerances have drifted over the years and so its maybe marginally out of spec or only able to handle lower margins and with the brand new train whose engineering tolerances should be spot on to begin with its messing it up, whilst the older trains trundling around for 30-40 years dont have that same precision