well probably the most obvious thing is the diameter where the filament fits is too big
but aside from that your hot end is too short so the heat travels as much up to the bracket as it does to the nozzle
it also looks like its stainless steel...great heat conductor / holder.... in this case a bad thing
The dome nut youve used as a nozzel is too long (A)< see attached pic which makes the heating element too far away from the nozzel exit point (
The black area (D) looks like an insulator when you should actually be cooling this area (fins and or a fan) and its too short (C)
Trim the nozzle so A is shorter ,Halve B ..Double C and get rid of D insulation and add fins webs anything that increases the surface area
My guess is area D is staying hotter than the nozzel itself so the ABS is more molten and the route to the top therefore has less resistance than the route too and thru the nozzel
Good luck