I had a similar problem, however when it shows it to be green in a said position, when i then place it it is placed opposite to the position the green was showing. so basically in certain parts of my castle im going to have concave curved towers rather than a regualr circle. I just wanted to add, i may not have helped your situation but now anone who sees this can see two problems.

Having this issue on my server. Have a hunch it may be a mod conflict.

when that happened to me.when i first started modding my server,i found it was cauesed by the server not being fully shut down when i updated .it takes a few minutes before it finalises its saves so it is better to wait for 5 mins then do the updates direct to the server.the other cause is a corruputed update it can happen .steam ocasionally can cause corruptions.