"Sudden devaluation" refers to a rapid decrease in the value or worth of something, like money or an asset. It means that its value has dropped significantly and unexpectedly. Full definition
And with good reason, as these points tend to give you the most options for redeeming with various airline and hotel partners, which protects you from sudden devaluations in any one program. (travelcodex.com)
First, they are not subject to sudden devaluations like miles. (valuepenguin.com)
As long as I'm not missing something (and I don't think I am) this is an underhand and very sudden devaluation to the Hilton Honors program that I don't think anyone saw coming. (travelingformiles.com)