I had the same happen in my base for a while, 2 signs and a lantern next to each other. Maybe you can find the old thread. A poster theorized that it was because your items are exactly at the limit of a "block" when the game renders the world, and when it renders your items it hasn't rendered their support yet so they break.

I dont know if it was really the reason. I ended up moving my things very slightly- like not even 1 in-game meter - and it stopped happening.