I had the same issue just now. I imagine it is a bug.
Nevalistis: This is correct. There is a bug with tornado behavior, and you’ll see this somewhat confused wandering with any Rift Guardian that summons tornadoes (Sand Shaper and Saxtris included). We’re currently investigating this issue.
To clarify, the tornadoes aren’t attempting to stay close to their summoner; they’re just changing directions too quickly. As a result, they won’t travel very far from their spawn point. The behavior of the enemies themselves should be unchanged so, in the meantime, kiting the Rift Guardian away from a cluster of tornadoes should yield more desirable results.
Not exactly the worst two Guardians there, at least not for their tornadoes. (Saxtris and his bug summoning, on the other hand…) Try not to die excessively, or get too used to the new tornado behavior, as it probably won’t last long.