[sumodm]

Yes, this seems to be one of the issues. Here is a talk by ISRO Chairman S Somanath at Indian Institute of Science (IISc) about the same and what they added. He goes into details of what went wrong. These are based on my limited understanding. One of the thrusters had an issue and got activated for longer (or may be activation profile of thrusters at its extreme's were different from modeled). They had a narrow landing region selected as final position (even one possible point). So now their control system tried to correct this but the algorithm had a bug and that caused it to be further delayed. At this point the correction required, i.e; thrusters to be activated, was outside the tolerance levels. So finally ended up with 50m/s vertical speed. https://www.youtube.com/watch?v=fZ2sNRP1opY&t=1440s

With new one, they did couple of things. Larger area to be selected for landing based on camera input. Escape sequence to more achievable points, if something like this happens again. They increased the tolerance from 10 degrees to 25 degrees and guessing fixed the bug in code. They also did some smoothening of the trajectory for different phases to make it more continuous. I think they also made other changes in engines among other things and a whole host of testing.