Problem with buttons.

Hi.Almost a month ago i've received my Japanese copy of Project DIVA F 2nd for the PSVita.I started to play,but,some while ago i've noticed something weird.
Like,yesterday,i was playing Melt,and i was halfway to perfect it.Almost the end of the song,i've started to get a lot of "WORST",even if i was tapping the buttons with the beat.And the same thing happen with Spoofing Ganger on Normal,on the second Technical Zone.This thing happened also with analog sticks.I don't know if it's just me(probably is)or my PSVita is leaving me(which is really weird,because i buyed it just a years ago,and the only problem i've haved was a problem with carger of the battery but i managed to resolve it).I hope someone can help me,because i would be really sad if i could not perfect/clear songs anymore.Thanks in advance. :) (and sorry if i did some error,i'm not good at explaining :/ )

 

I tried closing and re-opening the game, but this doesn't work...i tried even on PDf and even that seems to have the same problem...(other games make only uses of touchscreen so i don't think they are affected)so it's a problem of the PsVita itself?

 

I was tapping regular notes, but sometimes happens also with double and hold notes.

And yes