@Slarck Thank you.
Just check and add delay before and after pbhub.begin(), the program with only this library is very stable. However, the program with complete library set was not working.
I tried to remove it ne by one. Finally, I found somthing :

1. Every time have M5StamPLC.update(); the program cannot read data from Pbhub
2. I tried to add delay before and after every M5StamPLC.update(), pbhub.begin() Pbhub.analogRead(0), the situation is not solved.
3. I guess there is some trick while using pbhub together with SD card, StamPLC display , Digital Input scan. However, at this moment I still cannot make everything working at the same time.

@felmue
Thank you Felmue,
By testing the Wire interface and M5UnitPbHub seperately, I finally got response from the PbHub. I'm not sure what cause the problem. When I used your sample with the minimal code, the PbHub responsed and got analog data back after serval reset or unplug/replug the PortA cable. But it is not consistency working after each program download.
In my more complicated program with SD, PWR485 , M5StamPLC.Display , the PbHub did not work at all. But if I just put in I2C scanning code together with my program, there is response from PbHub that address 0x61 was found.
I think the problem is the command:
pbhub.begin(&Wire, UNIT_PBHUB_I2C_ADDR, 2, 1, 400000U) and
Serial.printf("0:%d 1: %d 2:%d 3:%d 4:%d 5:%d \n",pbhub.analogRead(0), pbhub.analogRead(1), pbhub.analogRead(2), pbhub.analogRead(3), pbhub.analogRead(4),pbhub.analogRead(5));

I am using STAMPLC and have all function included the PWR485 are normal. However, I purchase a PbHub to use as a extended input for buttons. I cannot connect the PbHub on PortA or PortC on STAMPLC.
I follow the sample code as follow in setup:
#include "M5UnitPbHub.h"
M5UnitPbHub pbhub;
void setup() {
Serial.begin(115200);
if (!pbhub.begin(&Wire, UNIT_PBHUB_I2C_ADDR, 2, 1, 400000U)) {
Serial.println("Couldn't find Pbhub");
while (1) delay(1);
}
}

void loop() {
Serial.printf("ch:%d adc:%d\r\n", 0 , pbhub.analogRead(0));
delay(1);
}

The following is the response on Serial Monitor:
Couldn't find Pbhub

E (1982) i2c.master: I2C transaction unexpected nack detected
E (1983) i2c.master: s_i2c_synchronous_transaction(924): I2C transaction failed
E (1984) i2c.master: i2c_master_multi_buffer_transmit(1186): I2C transaction failed

Wirings and functions are correct, G1 and G2 can get analogue and digital data I/O as normal. Any hints to solve the problem. I have write a simple I2C scanner program on Port A G2, G1 pin, there was response from Address 0x61, but Pbhub library cannot read data from Pbhub