Major Chao boss disappears

so originally i thought i killed it and it dropped nothing, but today i realized that it just straight disappears along with all the other piggies in the boss map. no idea why~ it's happened 3x now and i can't proceed with my kill count. please help!

 

can a forum mod up it from moderate to something more serious?

 

I've changed it to Major, but we are actively investigating the issue nevertheless. Thanks!

 

Thank you Sen!! :3

Idk if this helps but it only happens on one character, sometimes when Chao is nearly dead and sometimes not as close yet but always at low HP. It takes me waaaay longer to kill on this character than my other one so idk if the timer is a factor.