Since the American Wilds update medium and long log loads being carried by the log carrier + medium/long trailer method are sometimes becoming misaligned on the trailer end. The logs move partially away from the centre of the trailer and clip through the support post so the load appears to be balanced over the wheels on the side of the trailer. The mass shifts and this reduces stability. This has happened to me with the C-255 & C-260 hauling long logs and I have just watched a streamer have the same issue with the B-131 and medium logs, which induced a rollover. It seems similar to the old Spintires bug that occasionally had the load "fall off" the trailer completely and ended up being dragged along although still firmly attached at the front end. The load only fell off to the right side of the trailer (looking forward) in Spintires and both the events I have had and the streamer had the load shift over the right side wheels in Mudrunner. Not had any issues with this sort of thing in Mudrunner until now, even with around 1000 hours played.
I also see a related issue where the long logs are floating in the trailer cart. I saw it with the C-255. That's partly because the load is resting on a single log that's lower than the rest. Rotating the load so it rests more naturally I think would fix it. I don't think that's something we can do ourselves in the xml files as far as I can tell.
This is not exclusive to the update it hapened before too.
The visual doesn't reflect the collision model necessarily,it can be just a cube of the size of the load or in many case not as detailed as the 3d model itself to lighten the processing power required to run the game.
To have a better understanding of what hapen it would be interesting to have the real form of the load and the cart collision.