I know this is a late response but i found a fix. You just need to launch the task manager, go to the details tab and right click on "GTASA.exe". Then you have to click "set affinity" and uncheck every cpu except for CPU 0.

Now i don't know why this is the case but i have a guess. Back when the mobile port for gta sa came out most phones only had single core cpus (i think) and since the game is badly optimized and the windows store version is nothing but a shitty port of that version, they didnt even bother to fix any issues that would happen if they ported it to pc. so the game needs to use one single core to function properly. this is just a guess though and the reason could be something entirely different.