We are very well aware that students do not like this feature and students regularly request the ability to just reattempt what they got wrong.
We have, however, designed this feature very purposely, and can I take a moment to explain why...
HegartyMaths is all about trying to build the habits of a great independent learner, encouraging students to see that how they work is probably more important than the outcome of their work and that with effort over time comes success. Often learning is hard and frustrating but with time and effort it pays off (often not immediately but over a period of time). Angela Duckworth talks about this in her work on "Grit" and it's importance in developing successful young people.
Lots of things made for students nowadays give students immediate gratification (badges for logging in getting / something correct etc). Furthermore, the negative things that happen e.g. getting something wrong or losing a life in a video game are often 'softened' to make it easy for students to get over that mistake.
For example, in one of my favourite educational books (this changed my teaching career!)
it talks about just these things we are discussing. It mentions how students nowadays get really softer moments of failure e.g. in old computer games (like Mario) when you died at the end of a level at the last boss you had to re-do the whole world/level. This was incredibly frustrating and annoying but it was about learning to deal with mistakes/failure and cope. Nowadays modern computer games will restart you where you died in the game, in effect, meaning it matters very little whether you failed or not.
We have designed it this way so that in a really low stakes environment students can experience a little frustration but learn that it's ok to not get 100% all the time. Further, it's not always about getting 100% (often students think that's the aim of HM but that's not the aim). We think that it's better if they take their notes of the video and do their workings written out and get 80% (by making 2 corrections say) with lots of effort as it's ok to make 2 mistakes when you are trying (you can redo them in fix up 5).
Hopefully, you can understand the position on this and with an explanation to students, it might help them not be so frustrated or demotivated.