The Conda crashing bug is sort of a known bug.
It seems to happen when you hit "that" sweet spot located somewhere in the underbelly. Some people have suggested that it could be the power plant taking the hit, resulting in shortly delayed death, no matter the shield/hull.
I always enter letterbox at somewhere near 100~130 m/s, however I do not, under any circumstance, scratch the underbelly. I'd rather crash the whole thing nose first, or smash the flanks into the door or whatever there is to smash it on, than expose the underbelly.
Also I do crash-dock all the time. By smashing the whole ship into the pad (where it's flat) and hopefully drifting just the right amount, or by using the control towers/buildings to "nose-brake" - in case I really messed up my approach. No problems here.
It's really the angle from the letterbox. Well, it really "seems to be" the angle from the letterbox that manages to reach some... vital underbelly part. I suppose that speed does not help, but it's clearly not speed alone.
Edit :
This (that little scratch sound hurts my soul each time I watch it) :
[video=youtube;TRkYYgB6rbA]https://www.youtube.com/watch?v=TRkYYgB6rbA[/video]
Credits to Kornelius Briedis. Check
his YT channel, lot of great infos.
He was going at ~100 m/s at the moment of impact.
I can crash my Conda, with full cargo, with shields OFF, straight into the wall (literally, nose first), at 90 m/s, and only lose 17% hull (with military). So don't tell me this is a speed issue.