Problem 1 : voltage drop on 3V3

When the buck boost converter turns on, the output of the 3V3 converter drops by 200mV.  The problem is that the feedback resistors of the 3V3-converter are very close to one of the inductors of the SEPIC-converter.

Swapping the location of the buck-converter and the SEPIC-converter as well as choosing 0603-resistors instead of 1206-resistors might solve the issue.

Problem 2 : limited output current of SEPIC

At an input voltage of 3.7V and the output voltage of 5V the SEPIC only reaches about 500mA.  Efficiency is also too low, reaching only about 60%.