Had a bm x1 at the garage last year and the dpf was completely blocked. The engine would only run for only three seconds at a time unless you undid the differential sensor then it would do 5 seconds. Going on the quality of some parts made now I would look at the dpf filter being somewhat sub quality combined with being completely blocked.... An unfortunate accident caused by someone trying to help with a hopefully recognized product meant to do this job. But a dpf blowing its weldsIt "sounds" like your exhaust was blocked and the pressure built enough to split the welds on the cat and dpf........something I've not come across in 55 years of being a mechanic............as to who or what blocked it ...........