The "Westfield DF614" seems to be bugged as it doesn't attach properly and instead is quite floppy.
It also doesn't look properly attached when unfolded....
I'm using the "TLX Phoenix Semitruck" on "Modhub" (with the second extension) and the "Winkler Grain Box X2" from this mod (configured wiht the option "box divider").
this doesn't happen with your Volvo mod so im Using that one....