custom ESP32 board produces "garbage" on serial

[ESP_Sprite]

Also, in the Sparkfun schematic, the SRN output is fed into V_BATT, which is then goes through the BQ24075 to the (unregulated) putput of that board. You, however, connect SRN of U4 directly to the 3.3V rail. Obviously, that rail is then gouing to have the full LiIon voltage over it (minus the 10mV or so voltage drop over the 0.01 ohm R8.) You then feed this 3.3V rail directly into your ESP32 module. See attachment if the path is not clear. If you ever had a a fully charged LiIon battery connected to the board, this could have killed your ESP32.

[pietnl]

Thanks! I will ajust my circuit to fix that.

Do you think that could be the cause of the problem with the boards? or are there other steps I could take to fix the issue?

[ESP_Sprite]

Possibly. Results when running the ESP32 outside of their specs are undefined, and as I said, you may have permanently damaged something. Hard to tell exactly with the information given.