On my last project in Cinema 4D, I was animating particles with Thinking Particles and I animated only few elements but for whatever reason at that time, none of those keyframes were visible on my animation timeline. Impossible for me to figure out what was causing this. I was sure it was silly and yes it was: the automatic mode was off… to put it back just do Alt + A and all the keys will come back.
ALT + A = Automatic Mode (toggle)
Timelime – View > Automatic Mode