System: Windows 10 Pro x64
OS Version: 1909 18363.720
Game Version: 1.07.153006
I have a fairly massive base of Watchtowers creating a walkway in a 360 degree and I believe this mainly happens when I try to place them closer to the edge of the watchtowers or between them both.
I don't recall this issue prior to 1.07.
Update: This applies to backpacks as well (Only Tested With Field Backpacks), and happens anywhere on the 3rd Level.