I've searched for answers here and elsewhere but haven't seen this exact configuration.

Box has:
3 sets of black/white wires. 2 sets are old fabric covered and 1 set are newer covered in plastic---maybe this set goes to the switch?
2 fabric covered whites are connected to the plastic covered black in box
2 fabric covered blacks are coupled and connected to black in fixture
Plastic covered white in box is connected to white in fixture.

I didn't change this configuration and connected new fixture the same way with black to black and white to white but it blew the breaker.

Any ideas what's happening and how to fix?
Thanks!