statistics API Unusual

[valiner]

version v5.2.1

I'm using the statistics API of v2fly. When the traffic is large, the traffic statistics are reset to 0 after a period of time. I've looked through the source code:

type Manager struct { access sync.RWMutex counters map[string]*Counter channels map[string]*Channel running bool }

I didn't find any operation to clear the counters. Can anyone tell me why?