Connecting ESP8266 with STM32 Nucleo
You should not power the ESP off of the STM's 3.3&nbsp;V pin. You probably have a 500&nbsp;mA fuse on there and if your STM is running full load, maybe a couple of LEDs or other components on the board and the ESP together could exceed that fuses rating.

Get the LM1117 instead; it's a solid 3.3&nbsp;V regulator. Also put a beefy capacitor parallel to the ESP's supply, so when it starts building up its Wi-Fi network the current peak needed can be easily supplied.