Hey!
Here's an experimental pixel snap shader I've been working on, let me know if this changes anything: https://pastebin.com/qjn5grc3
Have you tried a different font and seeing what happens? Or try seeing if the same thing happens with Unity's default UI Text? When messing with this pixel snap shader, I found that some fonts had kerning values that made things line up in really odd ways, and that the exact same problems were happening with the included UI Text, too.
Also, try making the quality value match the size, and see if that helps at all? For UI text, the size /should/ be the actual screen size in pixels, so quality should match up with that. Also see if changing the filter from bilinear to point does anything!
The centred text having this all the time makes me think it has to do with pixel snap, so hopefully the shader is a good starting point? It's not perfect yet, but I want this shader to fix this problem in the next version.