As per a bug report from Pixomondo: if there are two static meshes in the scene and one has a rotation, it gets a GPULM bake artifact as if it is intersecting with the unrotated version of itself. See the attached photo for an example.
Please note that Pixomondo is hoping to receive a bug fix patch that will apply to 5.0. Maybe the fix can even go into the public 5.0.3 if it meets the requirements.
This occurs with a single GPU rather than multi GPU.
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-157346 in the post.