This is not uncommon. In my experience they tend to do this in higher humidity

I'm just wondering if the soil has enough nutrients left.

Mine do it every summer as soon as the humidity cranks up. Old soil, new soil, doesn't matter as long as that water's getting in there... At least it makes propagation a cinch -- you've already got rooted cuttings that you can just stick into the ground! (Because of this, I've got a bunch all descended from one parent plant -- I finally gave all but the parent and one tiny baby (just 3 segments long) away.)

Fairly typical for Schlumbergera.

If you suspect something is wrong with the primary roots, make sure they haven't rotted. This is a fine time of year to work on the holiday cacti, so don't be shy.

Josh