There are holes in the ground in various places. Water is not reflected.

S19 Near the ANCIENT RUIN area, the ground is missing in places, causing people to fall down from above.
Please fix this.

Also, the water on the floating island in I21 is not reflected.
Depending on the viewing angle, the water disappears completely.
Please fix this as well.

In a more detailed example, there are small holes in the joints of some of the monuments...

Hey no worries and thank you! I have a lot of fixes for little things like this coming in the next update. Big performance improvements and a couple new monuments as well.
Unfortunately I can't change how water works in game, that's entirely up to facepunch. Floating islands with water have a water culling volume underneath them that is necessecary to prevent players from swimming randomly under the islands. This same volume culls water if you look at it. I can probably nudge these around a little for the next update - It might help a bit. 
We'll have an update before forced wipe so if you have anything you'd like to call out in the meantime I'm happy to address more things you might find if I haven't already fixed them  

Changed Status from Pending to Work in Progress

It's a small detail, but there is a rock floating.
Please fix it accordingly.

Changed Status from Work in Progress to Fixed

Changed Fixed In to 1.2.4

All set in the new version. Feel free to let me know if you run into any other issues