Unity UI Unity 2018.2.[1,2]f1 - Introduced artifacts to UI sprites at runtime

Hello everyone,

First I would like to mention that I am new to Unity and that I haven't had the change to learn in the proper order. I was thrown to the wolves so to speak. The application I am working on is a mobile app, Android and iOS, very heavy on UI elements.

The project was created with Unity 2017.3 or so. I installed the newest version (2018.2.1f1) of Unity and as expected opening the project there gave me the re-import, API update, etc messages. Updating to 2018.2.2f1 changed nothing, the issue persists.

I am not yet sure if other issues were created but the most obvious is that most, if not all of the sprites (png files), used in the project have serious artifacts when they run both in the editor or a device. To be clear the artifacts appear when the app goes live. When editing everything looks fine. Also 2018.1 didn't seem to have the issue.

The images have alpha channels and it seems that the artifacts always appear in those areas (if I haven't missed something).

The sprite settings are:



Example image (the blue background is a different layer the image has an alpha channel):


The above is a series of images animated by an animator. As you can see the images are inverted, mirrored, with worse artifacts appearing etc.

To expand a bit:

• I did some research and found that a similar issue/bug existed some time ago where the Sprite Atlases were introducing these artifacts during the packaging. Can this be a regression?
  
  
• Playing around with the settings of the sprites I found that changing the mesh from tight to full rect seems to be solving the problem. What would the impact of that be (mobile app)?
  
  
• At a much older post in Unity's forums someone was asking if the sprites had alpha channels but that discussion didn't go far. Other images(spites) leak into this one because of tight packing? If so how come up to now it was working properly?

What is your take on this? If any more info is required let me know and I will try to provide as much as possible. Thanks!

UPDATE: Updating to Unity 2018.2.3f1 has not fixed the issue.

UPDATE: I have found the issue. Looking in my repo history I found that the update of Unity actually broke my Atlases. The settings were initially set to Full Rect but for some reason it was changed to Tight. That being said I wouldn't mind if someone could explain why Tight packing produces this weird behavior.