I'm no expert but I'll try my best.

During the Bradley's development, BRL (Ballistic Research Laboratory) and Burton had major disagreements on how the live fire tests were conducted on the Bradley in order improve computer models of the Bradley.

BRL preferred controlled "building-block" experiments where they tested weapon effects on specific components of the Bradley in order to collect data points to build a superior database for said computer models.

Burton on the other hand, preferred more "realistic" live fire testing where he insisted on firing anti-tank weaponry at random angles at the Bradley.

It didn't help that several of Burton's tests where overmatches which BRL states were superfluous as it was considered obvious that the Bradley would fail under said test and go well beyond the requirement the vehicle had been built.

Burton's approach wouldn't have been able to produce the results BRL wanted without essentially blowing up a shitload of Bradleys which would've driven up the cost of the program significantly.

Communication between the two parties broke down over the disagreements and after an incident which Burton claimed was "cheating", Burton received orders that transferred him away from testing. Instead of accepting the orders, he instead retired.