At the low sale price under $15 on the Summer Sale, it only made sense to buy the Diesel Legends of the Great Western DLC, and as a perpetual fan of shunting, am I glad that I did so. Today, for example, I took on the "5X02 Shunt Coach Set" session for the 08 shunter, which involves the slow (speed limit of 5 KPH in most yard areas) but sure formation of a passenger train in the Old Oak Common yards. Toward the end, I encountered a couple of unexpected oddities. The first involved a "vehicle possessing what might be called a Hogwarts annex: [I've inserted these as thumbnails: click them to see the full sized screenshot.] A second oddity occurred when I dropped off the completed coach set and discovered that I could not set some switches required to reach my next-to-last destination. Taking a second look at the 2D map view, I noticed another 08 shunter approaching my location; returning to the 3D environment, I watched it couple to my 08, since it could not reach the coach set. Evidently, I had not been driving fast enough! Puzzled, I exited the session and resumed it from my last save and repeated the final three maneuvers at a faster pace. Sure enough, this time it was possible to complete the session successfully. Despite these oddities (I refuse to pronounce them "broken" or, peggio ancora, "bonked"), I found this session excellent and am looking forward to driving more of those included in this extensive DLC package.
I had the same issue. I buffered up at only 0.5 mph but that was enough to make the coaches do this. Even stopping a few inches away didn't prevent the issue when I coupled up. I haven't reported it, I've got ticket fatigue. I have reported a similar issue however, where coupling the class 31 to the train at Paddington results in the locomotive derailing.
I don't know what sort of driver you have in mind, but when I bailed out of the session after that strange encounter with another 08 and resumed it from my last save point, those Hogwarts artifacts (thanks for the term, by the way) did not appear again. For that matter, I'd never seen them before that I can recall.
I think these artefacts have been an issue with GWE from the very beginning. It has happened to me, though while just driving on the mainline, but not in quite a while. I distinctly remember way back in 2018 when Matt was doing early streams of GWE that this very issue occurred somewhere along the mainline. I have no idea if there is a way to fix it, and frankly I thought it was fixed because I have not experienced it in so long, but I don't think this is a new issue. Cheers