The same happens to me in 1.16
there's a workaround
Yeah, I'm not even sure if the sample block code they give out in the Vanilla 1.16.0 Behavior Pack even works. It also affects every platform. Since my main reason for playing Minecraft is to make addons, I might as well quit Minecraft.
The water also looks red somehow?
Maybe set the format version to 1.16 in the block code?
This bug is back in 1.16.1 and 1.16.10