With this mod installed alongside Big Brother Bob's Plugin ( https://mods.factorio.com/mod/Big_Brother_Bobs_plugin ) allows radars to be built on water. Not a huge issue, but it seemed like something to bring up. I can give more details about the other mods I was using if needed.

False alarm; it must have been another mod after all as a bunch of mod updates has seemingly fixed the issue.

EDIT: it's still happening under certain circumstances; it seems the base bobs radars can be placed on water but then big brother in-place replaces them and those ones can't be placed on water.

It's super weird.

ok