It looks like Octane won't hold onto a focal length of anything more than 1200 after the first frame. I did a little testing, and anything over 1200 works for the first frame, then the second frame drops down to 1200. Other renderers don't seem to have a problem with it. This behavior happens with a brand new scene, one camera, one cube, no keyframes.
Checked in Octane 2019.1.5, C4D R21.
Technical Director - C4D, Maya, AE, - Washington DC