It's impossilbe to look into binoculars when crawling IRL, even in slowest speed. I guess the bug occur since Arma2 in 2009(in Arma1, you are unable to move a bit when taking out Binoculars.).
Similar bug regarding Binoculars: https://feedback.bistudio.com/T145027
1 Equip binoculars, laser designators, or rangefinders.
2 Press Z to get down/in prone position.
3 Use optics, (look into the binoculars).
4 Press W/S/A/D to crawl/move around(use the lowest speed, counterpart to press C to slow walk when standing).
At this point you should be aiming down the sight of binoculars while crawling, which is impossible when holding a rifle or pistol in game.