There are two Android devices which use MMEX through DropBox sync service. One of them had an error and then sync to DropBox with uploading damaged DB to DropBox. After that, another Android device asked to sync and download the damaged DB to itself. As a result, both of Android devices cannot open the MMEX DB correctly (.
My old (half year ago) DB backup version has 450kB. I see in support of my NEXUS4 MMEX has 2.8 Mb cache memory. Could the cache of MMEX in an Android device include previous (health) DB? 
I understand I haven't correct set on DropBox service to have a lot of previous copies of DB ((.  But I wouldn't lose my data for last half of a year(. I read on this forum about saving data of MMEX on Android devices until MMEX delete. Is it really?
Could you help me to rescue the database?