Thanks for your feedback. I noticed that bug too but couldn't fix it because I actually have no idea why it happens. It's rare enough that I ignored it but it happens sometimes.
For the distortion effect: it's a shader inspired from a "ripple" effect. If you look up tutorials for a ripple effect in unity you will easily find a few videos on the topic (I mentioned Unity but it's easy to apply that to other game engines too, it's pretty much having a circle move inwards and apply that to a normal map)