Strange Realm

So me and my friends have this realm that we play on its kinda like hermitcraft. and for a while our stuff kept getting grieffed. at first we thought that somebody was doing it but we all lived in the same timezone and were all pretty active so we didnt know what was up and the realm only had five members on it so we werent that many people. so to solve the mystery we put a mod on the realm that would automatically record every player who joined so we could see who it was... the recording didnt show anything but the next day there was more greiffing. at first we thought that somehow the realm code got leaked and somebody was joining and then leaving the realm. but then weird stuff started happening like random fires and people randomly dying while flying with an elytra. also stuff was missing from chests. and when we enter any structure(shipwreck, mineshaft, desert temples,etc.) we hear creepy noises. like footsteps and breathing....