As you can see in the following picture it says not enough space in random locations. You can even see several places where it happens this is just one example. Is this some plugin that may be causing this or is it a rust issue? Please let me know.
Not enough space in random locations
This is rust native building system, nothing related to plugins neither umod. Usually that means something blocks building in that particular place, but can happen randomly cuz facepunch suck ass.