Hi friends, the buck converter (SGM6029) can cause problems with sensitive peripherals: I could not filter out the noise on VBat to run a DCF77 receiver module. Sometimes there are also reports of problems with the ADC with very small signals.
I was able to save my project by removing the buck converter (just push it away with a pin) and installing a diode (e.g. 1N4148 SMD) as shown. This is not difficult and takes 10 minutes. Instead of 3.3V you now have 3.2V~3.5V (depending on the charge state) and ~4.5V during the charge state! You can enable the internal reference (1.45V) for the ADC.
I also took the opportunity to change the charging current for the charging unit, as 150mA is too high for small batteries. There for I changed R10 (yellow arrow): Original ICharge=24000/160K = 150mA, now ICharge=24000/482K = 50mA.
Wow, Welcome to the 3rd LEVEL
Excellent deduction, and Solution finding as well. Seeed Engineering may have to take a look and see if this is a systemic issue or just a wonky Batch?
I appreciate the extra effort and fine quality post. How did you solder?, “Hot Tweezers” or air? Very, cool indeed.
thanks for the kind words! It is sometimes easier to mechanically destroy components at both ends with a needle beforehand and then desolder the ends separately. I solder them under a microscope with a very fine soldering tip. I have experience with several hundred LEDs
I had to share this one… The BEST or even better picture is on the LINK… Everyone should hit your link and see this project … WOW
Thanks for the effort…WOW!
PJ 
