items deleting when i load up my game

everytime i load up my game and go into build mode, i find windows glitched, pillars gone and items in my build missing. i keep having to replace all of these everytime i open this build. and its not just this one build. it is across all of them. chair are missing, mirrors, microwaves, tables, a bookcase i spent 2 hours cluttering. gone  ;-; please help me figure out why this is happening