https://www.youtube.com/watch?v=W3Ao3fUeU1Y

Stages descriptions:

00:00 - for some seconds at the beginning of the video, all running fine, walk is walk, run is run (even when crouch)
00:06 - apparently without reason the run animation is ok but the character speed is slowed down
00:41 and 02:08 - two game reboot don't solve the problem: the only difference is that the "run animation" is not shown anymore, left shift ignored
03:15 - apparently without reason the run animation and the character movement speed become inverted: when running goes slowly, when walk goes fast!