The implicits catsKernelStdPartialOrderForVector and catsKernelStdHashForVector (here) are ambiguous if A has both PartialOrder and Hash instances, and we're looking for an Eq[Vector[A]]. (List seems to have the same problem.)
I am not sure if we can fix it for Scala 2.11 without breaking BC. We might have to leave it as is on 2.11 and do a scala version specific fix for 2.12+. Or we simply drop 2.11 which is more likely now than before.