Notebooks LOST and a notebook "conflict" appeared

Guys, a notebook containing more than 80 notes dissapeared when I was checking it just now!!! And there is a notebook “conflict” now on android phone with 54 notes in it. I am in chaos and despair now. What can I do?? Is there a history version that I can return to?
I’m running a Joplin 1.0.175(prod, darwin) on Mac and Joplin 1.0.312 on Android.
The joplin on mac says synchronisation completed the day before yesterday, at that moment I didn’t notice this problem, while joplin on android has auto-synchronised just now.
There is a possible reason ---- my android phone has just nearly run out of space, with more than 500 MB remained, and I have managed to solve this trouble.
It seems that joplin can keep the history of at least 90 days. Can I return to the history status where no conflicts occurred?
Please help me! I am really looking forward to tackle this dilemma, because these notes are so vital to me.

If you don’t know what’s happening, neither can we. We can’t know why your notebook was deleted, on which device and when or why.

The only way in this case is to start over clean. Clear the data on your sync target, uninstall all the mobile apps, clear your desktop profile. Then starting from the desktop app, reimport your latest backup and sync.

Alright, thanks for your reply. That situation then was too complicated and might be caused by multiple factors. I have been trying to recover those notes today.
Anyway, thank you!