I had a water elevator that I constructed in my base. I placed down kelp plant blocks to turn the flowing water (from a water source at the top and in random places inside) into full water sources. Upon completing it and breaking the kelp, I noticed that there were places inside the water column flowing like topwater, but it was still underneath other water blocks themselves. I then continued to use my watervator only to realize that the water was invisible, and the drowning bubbles were not appearing on my screen, but I could still see the bubbles from the soul sand and I was still swimming upwards. This is clearly not only a visual bug, as I was also not drowning while inside this "hollow" water. It would appear that this effect started when I removed the kelp and updated the water.