I recently started Trials Fusion on the Xbox One. Wanted to go for the achievements yesterday and both the original Squirrel Achievement and the one for doing all track challenges unlocked too early.

"Bright-Eyed & Bushy-Tailed": Unlocked after finding 19 squirrels instead of 20 (the one on Jungle Gymkhana was still missing and I hadn´t encountered any of the DLC squirrels)

"Is There Anything You Can't Do?": I did all the challenges from Greenhorn´s Grove to Rainforest Rumble, skipped Expert´s Club and then went for the extreme track challenges. I think I got a bit more than half the extreme challenges when the achievement unlocked. At that time I had done exactly one challenge on the Expert´s Club tracks and maybe 5 across both DLCs (even including the DLCs the overall number of challenges finished was still not enough to unlock the achievement)

I remember that on the 360 I actually had to do all challenges and squirrels to get the achievements.
I don´t know if that´s a known bug, just wanted to let you know...