I'm having issue with this.

Invisible grass, but only in this mod's structures. Grass is fine everywhere else. Only a problem in the generated structures.
I have no idea what could be causing this bug.

I also had the same problem.

I have the same issue, here is what I could find out about it after a couple of tests : switching from the default texture pack to a custom one (only tested with DBcraft) OR switching from a custom texture pack to the default one will fix those blocks for me.
Going back to the main menu, or re-launching the game will NOT fix the issue.
Also, after fixing the blocks by switching texture packs, the issue will come back after re-launching the game (doesn't seem to matter if the game is launched with or without a texture pack).

Hope this helps investigate the issue. Looking forward to enjoy those nice buildings.

Could you send the link of your modpack or make an export of it to test this?

similar issues with better foliage installed. why even does the mod add its own grass?

So I got around testing a modpack with better foliage on and I got the exact same issue.

So I disabled Better Foliage and tested again and the visual glitch is gone.

I can safely assume that is Better Foliage causing the visual glitch.

Issue seems to come from the [connectedGrass] function, turning 'enabled = false' fixes this in the config