FireBeetle ESP32e + 18650 + solar panel

Hi,

I'm powering the FireBeetle ESP32e with 18650 battery and it seems working OK.

When wake up, FireBeetle reads 3x soil moisture sensors + 1x BME280 and upload data via MQTT before goes back into deep sleep. 

For testing, I run this at 30 second interval for about 12 hours:

(top 3 lines are the soil moisture sensors, thick red line in the middle is the temperature from BME280 and lower green is the voltage from A0 pin.)

I have some questions:

1. As you can see above graph there is a gap between 21:30 to 22:00 where the FireBeetle failed to wake up. I had to manually press the reset pin to turn it back on. I've experienced this a few times while I was testing with 18650 last 2-3 days. The battery level was about 3.9v which is within the FireBeetle's operating range. Any idea what's wrong?

2. Can I safely cut the "Low-power Solder Jumper Pad" for saving battery power during deep sleep? For an IoT sensor I don't need the LED.

3. After the battery test, I'll move on to the solar panel connection. I'm considering a 6v solar panel and for the connection I've purchase the followings: DfRobot Solar Charger v1.0 and TP4056 but not sure which one is suitable. Can you advise?

4. I notice that the FireBeetle onboard battery charger is TP4056 as well. I'm not sure I need another TP4056 for solar panel connection. Can I connect the solar panel directly to FireBeetle's VCC?

Thanks!