Apparently, the higher your framerates are, the higher you're taking damage from enemies. It's somewhat similar to Valkyria Chronicles' interception fire bug from back then.
All credits due to Wesker for finding this out.
From the looks of it, at 60fps (which the majority of PC gamers would play at) Sam would stagger after 3-4 seconds.
I've tested this multiple times using the AR mode tutorial (the bit where enemies shoot at you a bunch in order to demonstrate auto AR) and you take much more damage when playing at higher framerates. If you lock the framerate to 30FPS AR mode will activate after 6-7 seconds of taking enemy fire but if you're playing at a much higher framerate, like 144FPS, it will activate in just 1-2 seconds.
Note the number of times Sam staggers.
This can be consistently reproduced.
This is somewhat an interesting bug.