Open any project
Create a new texture array and add any 2 or more images.
Open one of the images in paint and alter it in someway visually so it is an obvious change across the whole texture + save.
Go back to the UE Texture Array, hit reimport, nothing changes.
Go to the texture itself and reimport->It will update with the changed image.
Again hit reimport on the Texture Array asset -> still nothing changes.
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-119368 in the post.