To clarify, using the Charge Rifle while rodeoing a Titan will generally only net critical hits on Atlas Titans. For whatever reason, it does not work on Stryders and Ogres to the best of my knowledge. Shooting with the Charge Rifle at range and hitting the critical spots works fine otherwise for all Titans.
It's possible Respawn patched it to work across the board, but I don't recall anything of such in the patch notes. Would explain why it works, or maybe it's like the case of Brain Surgeon where just about anything will muck up having your actions count towards the challenge.
And I feel for you MaGlock. I got lucky in my last couple of matches to where I'm 14 or 15 down on Freshly Squeezed, but so many people use auto-eject, nuclear ejection, or ditch their Titans before they doom to where. Also have run into a funny bug a few times where a Titan will be in doomed state with no ejection actions being taken, but I can only melee it and cause damage instead of executing the pilot. Will record it the next time it happens to see if anything else is going on at the time to cause issues.