The Rusty Ladders from MalisisDoors are invisible. I'm not sure if it's due to Optifine (or one of it's options) but I will test all of those options and see if this is resolved.

https://aeswere.ca/images/gktfev.png - Proof

Adding Optifine is known to introduce a number of render glitches and is considered a modification of the pack.

work around: play despite glitches or remove optifine

From the DigSite FAQ https://github.com/wideblaze/DigSite/wiki/Frequently-Asked-Questions

Q: Can I use Optifine, shaders, resource packs?

a: Using these might uncover hidden blocks or cause render glitches esp. when using portal gun. However, if you are ok with these minor issues then yes.

Alright, thanks for the answer.