Leads in custom views are mixed together (out of the blue for no reason) !!!

Leads in custom views are mixed together (out of the blue for no reason) !!!

I had Three different lists of leads thousands of names and contact information all sorted correctly and when I arrived to work this morning all of them were mixed for together for seemingly no reason at all. I did not do anything to change there location. Why would this happen? When I attempted to move them back to the proper location most of them were lost completely. why would this happen?  I have read on the forum list that this has happend to others too. Is there some kind of update that Zoho does where it changes the location of the information? Weeks of contacting leads is now completely lost. This has to be the most frustrating and not user friendly software I have ever used.