Nodejs driver for mongodb enter infinite loop to function ensureMinPoolSize

I use the official mongodb nodejs sdk with code

const MongoClient = require('mongodb').MongoClient

at the beginning, db read works well , however, after a while, code enter an infinite loop to function ensureMinPoolSize (see picture 1), is there anything wrong?

more info:

(1) my code is multi-thread (8 threads), every thread can read db,

(2) db pool setting as picture 2,

image