How could the plane have gone from 0° bank angle to 45°-90° bank angle WITHOUT lateral course deviation ?
If the wings were pretty much unloaded, quite easily. You need an angle of attack on the mainplane to generate lift in order to accelerate away from the course you’re on. If the aeroplane was in a bunt, which seems to be the case, it’ll rotate about the longitudinal axis and that’s about it, a bit like an aileron roll. This was not a “balanced turn”.
In some ways this is good evidence that something was seriously wrong in terms of stabiliser and/or elevator position.