Did Arius say that the Son is mutable?

Arius himself wrote that “the Son of God … is, ***like the Father, 'unchangeable***’” (Rowan Williams, page 96) but Athanasius wrote that Arius taught that the Son is “***like all others … subject to change*** … because he is changeable by nature” (Contra Arianos(v), RW, 100). Are we able to reconcile these statements, or did one of them lie? For one possible answer, see Rowan Williams pages 113-116 , beginning with the phrase "This leaves the third point noted above as a major theme of Arian exegesis to be investigated ..."