Wide angle (UW) HDR has crazy artifacts

I have seen the same myself, and posts from other users on this issue.  A developer told me the reason for this:

"the scene has very high dynamic range (bright lights and shadows), so the bracket EVs are far apart i.e. there is large variance in noise between the brackets."

Motion can make this worse: "motion causes ghosting and over exposed areas will blend in the dark shot which apparently contains lots of noise."

If possible, try to hold still, and tap on the darker part of the scene in the LR Camera, or drag your finger left/right to manually adjust exposure compensation to see if you can improve final results.  "The trouble with such scenes is exposing it correctly - when taking an HDR shot, the bracketing is based on the exposure currently set in the camera (which I think defaults to the point in the middle). This is often not optimal"

I hope this helps a little.