The Earth's inner core was rotating faster than the crust, so the core was rotating relative to the crust. It's rotational velocity HAS slowed to about the same speed as the crust... and it will slow down more than that over the next 30 years or so.

This is NOT something to be alarmed about. It happens on about an 80-year cycle or so where the earth's core rotation slows down or speeds up again relative to the crust. From what I understand, it's perfectly normal cyclic variation.

The earth's core does NOT go into "reverse". It simply slows down or speeds up rotational velocity vs. the crust... but always rotates in the same direction. Never reverse.