Heyo everyone!
I'm the creator of the video so I thought I would add a little bit more to it!
It turns out that the memory issues occur even just playing through one mission! I think it has to deal with more enemies loading in and not deloading properly, eventually overloading the game. Some people didn't have this issue, so it might be hardware dependent, but playing on the previous patches, my memory usage would stay stable at around 58% while recording throughout gameplay, while on the current patch it would continue to rise until the game will crash.
There also exists a progression bug where completing two missions in a row on Halo CE will force you back into main menu, but if the memory usage is high enough, the game will crash instead.
It is also notable that trying to close the game with task manager because of the memory issues will take an extra amount of time for an odd reason to try to clear it, with it being a lot longer than it should normally.
Overall, the patch has a lot of issues, particularly for speedrunners like myself, who all have to play on downpatched versions due to these differences and abnormalities. However, there are now a few speedrunners on the development team so I hope to see issues such as these get fixed in the near future.
Also, I don't know if it is applicable but if any 343 employees on the dev team want a rundown of issues within the campaign, lots of speedrunners have a long list of issues that we would like to see get fixed from the various games.