latency goes chaotic on every certain time (tonberry server)

has been like this for 2 weeks now

on every certain time there is this 2-3 hours window where suddenly my game connection goes really bad, on ping window it just full of RTO and the latency spiked up

it seems only happen to jp server because during that time my internet is fine, website is up, stream is fine, youtube is smooth, even when accessing other server like NA server is also allright

it only on JP server at certain time, my ping goes bad. can anyone help or at least explain why this happened?

i just want to know if this is from my end or from their server?