Why do my stats momentarily change?

I'm running a seasonal Crusader with my own variant on the Akkhan Bombardment build. I noticed a strange issue that occurs when I change gear or Kanai's Cube slots, in which my main stats (Toughness, Recovery, and also Thorns (which is important for this build)) go up OR down, and then almost immediately drop back down or go up again. This all happens within a second or 2.

The following stats are all when switching ONE Kanai's Cube modification at a time, and are shortened for this post, but the numbers are all the same anyway:

Toughness: 47m > 22m > 33m > 47m

Recovery: 4.4m > 3.2m > 4.4m

Thorns: 222k > 316k > 253k (this is with a Thorns based item, so the end result will be higher)

Why do these stat changes occur? Is it calculating something else based on maybe the Ring of Royal Grandeur, which reduces set cost by 1? It's kind of frustrating to see, as I'd love for my thorns to be at 316k, but it drops down quite a lot almost immediately.

EDIT: Sets in use:

5 Pieces of Akkhan

2 Pieces of Captain Crimson

2 Pieces of Invoker