@marco you mention you changed the power source, what are you suing for the ESP?
You can flash an ESP with the power from a Nano but you can’t run an ESP from it.
BLYNK_DEBUG in itself can be the problem so it’s only recommended for debugging.
Try 9600 baud rate for ESP (19200 should be ok for Serial Monitor).
Ensure you use any frequency based widgets as PUSH frequency not timed frequencies.