Injuries / muscle strain during bench

[Visagex]

About 2 weeks ago I was benching and during a x3 heavy set i felt like what a strain would feel like it my lower back to the left of my oblique ( lower back ) and was out of the gym for like 4 days the next morning I could barely even turn my neck to the left.

I kind of put it off like maybe my form just slipped, today it happened again. As soon as I felt that familiar pain I racked the weight tho so it doesn't hurt anymore but I'm wondering what is the cause of this?

Strength indifference in my back?
Bad form? I personally think my form is great, I've watched many videos and I've been training for about 6 years now.