We usually hear it used as an uncountable noun but, according to the dictionary, it can be used in the plural in the sense of "information or report, especially when communicated from a distance: Advices from an ambassador." That use, however, is somewhat rare. I have encountered such a usage only a few times in my life.

it's uncountable

It's uncountable - it represents an unmeasured collection (same with information, evidence, housework, etc). I'm also surprised by "advices", but I'd interpret it as a condensed form of "pieces of advice". Still, I'd question a person's reason for using it.

uncountable