I'm not sure if you are trolling or not but just in case, he down patched the game

If you want to speedrun this game I recommend you check the resources tab and download either goldsource package or 2005 WON version which comes with BXT and it has all features such as proper demo recording. And no, bxt doesn't work on 25th anniversary version. Either way I recommend you try those other versions of hl1.

Stay closer to the corpse when you hit her for the first time

There are few maps that load pretty slowly, it's mostly c_start2, apartments and asylum (right after the gates)

Load them at least once before the run

In the "saves" folder, no?

Maybe. Level 1 route can be even better. Level 3 can also be slightly optimized, level 4 is rng based because of scout and I barely practiced level 5. I honestly want to make an autosplitter so times are going to be same for everyone and will be much more fair but I don't have any cheat engine experience. One day maybe.

Try launching autosplit as administrator

I have windows 10 and it still crashes once in a while

Unfortunately, you can't really remove it. You can use RInput injection but if you do your GUI menus (like code panels) will stop working properly. This is basically a bug with hl1 and its mods. If only this game was build on a slightly newer gldsource engine you could use m_rawinput bind to enable/disable it or maybe even there would be no bug like this but it's your life now.