Please provide a step-by-step process of how the bug can be reproduced. The more details you provide us with the easier it will be for us to find and fix the bug:
Build a roof.
Wait for server restart.
Most of the roof gone with the wind.
Every day the roof loses stability when the server restarts.
Not sure to understand how you made your construction under but I have encounter very similar issues. It was related to adding pillars from up to down (from under a roof to another structure) to increase stability of my build when it was not possible to build from down to up*. At server restart it seems to it rebuilds your structure from ground/foundation to top (or something similar) so if this “pillar” is required for the stability of the roof to be above 20, when the server try to place the roof, the stability is not there yet because the added pillar(s) to not provide yet the extra stability.
*Example can be going down from the middle of wedge surface to a square one (and you end-up not on the middle of the square one). Even if when you do it, it provides stability, it is not working when the server rebuilds it.