Very strange print issue only for a few layers

Hoping someone can point me in the right direction on the issue shown in the image.

I have printed many of these before and have now upgraded my anet a8 to the am8 with a genuine e3d hot end and bondtech extruder. For a couple of layers i have that issue that looks like its over extruded but then it prints as it should. has anyone ever seen something like that?

Thanks