Warnings problems of the 2021 Subaru Crosstrek

While driving on the highway in the slow lane (furthest to the right), traveling at approximately 50 mph, I came to be behind a tractor trailer. Before I had a chance to pass the tractor trailer, it switched lanes abruptly. My vision past/beyond (in front of) the tractor trailer was heavily obstructed by the massive vehicle itself, so I could not see that in front of the 18-wheeler there was a mid-size sedan traveling at approximately 5-10 mph in the same active highway lane I was in. I had almost no time to react, and neither the automatic emergency braking system nor the forward collision warning system engaged. Both of these systems should have activated to prevent the collision and/or minimize injuries and damage. I subsequently collided (harshly) with the aforementioned sedan.