I've returned mine for an exchange to B&H Photo who issued me a RMA (They paid return ground shipping too.). I'll chalk mine up to decentered or tilted optics as mentioned in some other reviews where they also got a replacement and amended their review.
Mine would not reach infinity targets by turning the lens focus ring. It hit the stop prior to getting there by maybe 2mm. The infinity icon was way far to the right of the index mark too, maybe 6-8mm. It should be aligned better than this, imho. There are reports of the lens being soft in the corners along with a strong two-stop vignette at the corners when wide open, and it gets less intrusive stopping down.
I'm hoping the replacement has more latitude at the infinity stop location and the index mark location is better indexed. It was an early model at serial 2950 so we'll see. It is a nice lens otherwise, even with a bit of barrel distortion that can be corrected in post with software. I'd like to see DxO Optics Pro address this lens down the road as they can take care of some corner softness and the strong vignette and barrel distortion as lenses are what they primarily do.
I also contacted Venus Optics and sent them the images as well as questioned them about the hot-swapping matter that Olympus says not to do in their manual - although people do it anyhow and I've done it at times with my DLSR. The X5S gimbal doesn't seem to like doing it by the noise it makes during the switch. They are looking into the infinity and soft focus, but nothing on the hot-swapping was mentioned. GO 4 acts goofy with it at times and I've seen f/1 on the screen along with a very slow (~30 seconds) drift of the exposure while watching the histogram change when you do change the exposure. Less problematic with video than manual settings for me too. It really should have been chipped, imho, for the price which might may it play better with the current version of GO.
Venus Optics offers a 3 year warranty, but not having a USA based repair facility I don't know how they handle it. Shipping to China is very expensive, but not so much them to us.
Added:
I'd like to see how this lens works on an Olympus or Panasonic MFT body as to the still exposures and video too. I may end up buying a Oly. Pen-F body since buying all these MFT lenses for the X5S. I like their smaller size and weight.