Thanks @Michael_Coburn , I am suspicious about mongodb_exporter. Since I can confirm there was no error at infrastructure detail and all my MongoDBs were journal:enabled(which means not in-memory use), there is only one thing left. I tried to upgrade PMM but there is an existing bug at mongodb_exporter so I could not and still waiting to fix it (Problems after upgrading from 2.9.0 to 2.11.1 - #13 by Ghan)
At last 3 images, it seems exporter or PMM follow metrics 1hour back? Is not it strange? Also there were no inserts but still got latency spikes?