Just had a weird thing happen to me - I've crossed YYZ T1 preclearance many times with Nexus with no problem, even with the new GE machines. Today, I walked up to the machine, it recognized a human has arrived and took my photo. It asked me to scan my travel document so I put my US passport in the reader. After a minute or two, the screen lights red and tells me to see the CBP officer.

Went to the officer, got asked a few standard questions (where are you going to? where do you live? why were you in canada? how long were you here? what are you bringing? are you bringing food?) and was let in to the country

Really super duper weirded out and curious why the machine would give me the red light especially since everything was fine when I used the machine at YYZ T1 preclearance last month