The new feature fallen logs do spawn on the water. The issue can easily recur.
Zeta Version: 16 Quark Version: 440
Here's the log: https://pastebin.com/zvvbpPb3
I do paste a picture here, but I cannot preview it here.

here is the seed of testing world: -4428278914085286715 (for better recuring)
the wrong logs spawn on the river.

Experiencing this as well, though I am using Tectonic (https://modrinth.com/datapack/tectonic)