That is looking great guys! I now have a few questions for you…
First is the water surface viewed from below, I’m guessing you added in another one sided material plane to get that effect while underwater? Or are you changing the base material values while underwater? I’m trying to decide which way to go on that, leaning towards modifying the material since there are already 2 plane meshes.
Second, those light shafts look great! Was accomplished using a mesh plane “godray”? also are they placed manually or are they particles?
And of course the caustics, did you guys use a light function? Or is it added to the sea-floor material itself?
You guys are doing a really job!! Thank you for posting up these videos here as well, it’s great to see your progress on . 
That is really strange, I thought I had fixed that prior to uploading. They are 2 redundant variables which I removed from the blueprint, and then deleted the struct type they were created with. Somehow they were still referenced by the BP even though I had deleted them first, causing error message.
Long story short, just press OK. They do not actually exist, so there is no harm in removing them. has already been fixed in the version.