I believe now Mo Ladak the site owner, uses more videos to introduce topics with a flipped teaching approach. Perhaps he no longer stores some of them on his site.
There are certainly many still there so follow this link for PURE A level maths linear graphs and equations for example:
He uses Twitter extensively now too it may be worth asking him tweet @mathedup, there is a link on the website home page on the rhs:
I hope that this helps.