This is really simple to reproduce. go ahead and hold your sprint key, and spam your forward movement key, aka (W).

You after about three seconds let go of your sprint key, and keep spamming forward. then after another 3 seconds just hold the forward key. You will notice the screen continues to bobble.

I believe the game still thinks you're sprinting, so even after releasing W it sorta goes in and out of sprint making the FOV bobble.

This is just a cool bug I found in the game.