I always updated Fuelio from Google Play Store (where can I find the standalone???). My phone is a stock one, without rooting nor strange things, and I paid for pro version months ago... 

I know what I did: I opened Fuelio (3.8.0), went to export database to SD and made a backup to my Mac via USB. And there's two options: the backup didn't work and the fuelio6.db existed becase of a previous one, or the backup didn't work dumping an old database version. As you can expect, I didn't care how Fuelio works internaly, I only know that I made a backup and didn't worked...

I restored renaming to fuelio7.db, imported, exported to CSV, cleaning app data and importing CSV again...

I don't have a CSV, only have he fuelio6.db backup... I need to convert fuelio6.db to CSV to import it...

Anyway, I don't understand this "relialability". If making backups of databases are insecure, don't allow users to make this. We trust on this backups, so has now sense allow to make a dump that can't be restored (even with paid version).

Hi again

I found a solution: used Root Explorer (it's the app name, phone not rooted) to find Fuelio exports and found in /sdcard/Fuelio but when connecting to my Mac I don't see this folder. "Real" path is /storage/emulated. Phone is a Nexus 5 with Android 5.0.

Anyway, renaming file to fuelio7.db, importing it and reopening the app worked for me. 

I hope this details help you to find and fix the problem...

Thanks