This is very annoying, I've been stuck at level 10 for around 4 times just trying to reach level 13, and then just now, I've repeated being level 15 thrice already when I should've been level 16 this is really really reaaalllyyy very annoying and frustrating it just makes you lose your mood into playing the game

Got the same bug...
http://www.gamesas.com/forums/viewtopic.php?f=40&t=23036&p=253820#p253820

we have exactly the same problem, getting weapons and upgrades after the roll back . I wonder what is causing this, really annoying, enjoying the game and all of a sudden it just rolls back to a lower level