Further testing has revealed that the AC Measure unit will shutdown at low current and will return completely inaccurate power values. This could be fixed in the firmware but there is no information on how to access and update the firmware and M5 Stack does not respond with any information to date. The AC Measure unit is useless for my purposes and I will see if I can access the firmware and write my own.

I tried it with several ESP32 Boards similar results, currently testing with a TTGO T-Display board using Arduino and Board Type ESP32 Dev Module. It uses default 42H address I2C same result if I power the device with external 5V or through the ESP32 Board.
For initial testing I connected it to a 20 volt AC transformer and am using a 1K 1Watt resistor as the load. So I expect it to return 20VAC and about 20 mA current.
I used the demo Arduino code supplied by M5 Stack in the AC Measure library. However, I replaced the display output with Serial.println statements since I do not have the display used in the code. The code outputs reads the values once per second.

So this is the output, sensor.getready() is used to signal if there are new values to read. Notice that the voltage and current and power factor are correct; however, the power value is incorrect and shoud be W = I * V therefore 0.02 * 20 = 0.4 A but as you can see it starts at 6.5W and counts down until it gets close to the proper value and then it stops responding (although you can still read from the device but the values will never change and sensor.getready keeps returning 0) If you power cycle the device (not the ESP controller board) it starts the same sequence again. Also notice before the Red LED turns off the power factor which should be 1 for a resistor starts to change as well.

It is as though the microcontroller on the AC Measure device keeps responding but some other IC perhaps used for measurement is bad and fails after a short time, either that or there is a bug in the firmware?

sensor.getready = 1, Red LED is ON.
11:25:01.898 -> Voltage: 20.35V; Current: 0.00A; Power: 6.50W; Power Factor:0.00
11:25:02.887 -> Voltage: 20.35V; Current: 0.02A; Power: 3.61W; Power Factor:1.00
11:25:03.908 -> Voltage: 20.18V; Current: 0.02A; Power: 2.50W; Power Factor:1.00
11:25:04.938 -> Voltage: 20.18V; Current: 0.02A; Power: 1.91W; Power Factor:1.00
11:25:05.984 -> Voltage: 20.18V; Current: 0.02A; Power: 1.54W; Power Factor:1.00
11:25:06.983 -> Voltage: 20.17V; Current: 0.02A; Power: 1.32W; Power Factor:1.00
11:25:08.013 -> Voltage: 20.17V; Current: 0.02A; Power: 1.13W; Power Factor:1.00
11:25:09.033 -> Voltage: 20.20V; Current: 0.02A; Power: 0.99W; Power Factor:1.00
11:25:10.084 -> Voltage: 20.20V; Current: 0.03A; Power: 0.88W; Power Factor:1.00
11:25:11.118 -> Voltage: 20.20V; Current: 0.03A; Power: 0.80W; Power Factor:1.00
11:25:12.108 -> Voltage: 20.21V; Current: 0.03A; Power: 7.34W; Power Factor:1.00
11:25:13.169 -> Voltage: 20.21V; Current: 0.02A; Power: 3.85W; Power Factor:1.00
11:25:14.184 -> Voltage: 20.17V; Current: 0.02A; Power: 2.70W; Power Factor:1.00
11:25:15.195 -> Voltage: 20.17V; Current: 0.02A; Power: 2.02W; Power Factor:1.00
11:25:16.244 -> Voltage: 20.17V; Current: 0.02A; Power: 1.62W; Power Factor:1.00
11:25:17.259 -> Voltage: 20.21V; Current: 0.02A; Power: 1.35W; Power Factor:1.00
11:25:18.270 -> Voltage: 20.21V; Current: 0.02A; Power: 1.15W; Power Factor:1.00
11:25:19.307 -> Voltage: 20.21V; Current: 0.02A; Power: 1.01W; Power Factor:1.00
11:25:20.313 -> Voltage: 20.20V; Current: 0.02A; Power: 0.91W; Power Factor:1.00
11:25:21.334 -> Voltage: 20.20V; Current: 0.02A; Power: 0.81W; Power Factor:1.00
11:25:22.368 -> Voltage: 20.21V; Current: 0.02A; Power: 0.74W; Power Factor:1.00
11:25:23.384 -> Voltage: 20.21V; Current: 0.02A; Power: 0.68W; Power Factor:1.00
11:25:25.438 -> Voltage: 20.18V; Current: 0.02A; Power: 0.58W; Power Factor:0.97
11:25:26.495 -> Voltage: 20.18V; Current: 0.02A; Power: 0.54W; Power Factor:0.90
11:25:27.510 -> Voltage: 20.18V; Current: 0.02A; Power: 0.51W; Power Factor:0.85
11:25:28.727 -> AC Measure Unit Stops responding; sensor.getready = 0, Red LED is off

I have the AC Measure Module hooked up to an ESP32 board (tried it with external 5V power or 5V from the ESP board no difference) when I turn on the power a red light appears inside the module and it works. However after a short time (15 to 20 seconds) the light goes off and it nolonger works (sensor.getReady() returns 0). I can then still read values from it but the values never change even if I change the voltage.
If I turn off the 5V power to it and turn it back on it will work again for a short time...

Question is:
1: Do I have a faulty AC Measure module?
2: Is this a known problem?
3: Does it need a firmware update?
Anyone have any information on how to proceed with this?

Thanks.