When minecraft is maximized in a 1920x1080 monitor, buttons look like this:

Making the game window smaller, buttons draw correctly:

Also, when you are in one of the World/Feature/Survival properties screen, resizing the game window by click drag of the window border or by clicking the maximize/restore button in the top right corner, the UI goes back one menu level.

BEFORE:

AFTER CLICKING MAXIMIZE BUTTON IN TOP RIGHT:

Hm, that's really odd. I test at 1920x1080, and have never encountered this. Could it perhaps be related to the resourcepack?

I will set up a clean install with only your mod and report back. I am not using any resource packs anyway, but I do have 100+ mods besides this one.

It still happens when the only mod is Terrarium.

Full log: https://paste.ee/p/pMAPM

Make the window bigger:

Resize width a bit:

More:

More:

F3:

Maybe it's the Intel UHD Video?

Hmm. Not sure why I don't see this issue at all, definitely could be weird specific GPU behaviour. However, I have found a solution that should resolve this.