@rafael other common issues:

* sometimes external sensors take time to power up, if your firmware tries to talk to it immediately, sometimes it will hang. This isn't an issue if you flash the chip, because all the stuff already has power
* If your linker script isn't exactly right, sometimes running after flash will work (because the debugger starts from the right location), but the normal boot sequence doesn't work
* Like Lumpio mentioned, if you have configured rtt-target or something manually to block
* Depending on what your panic handler is, sometimes `panic-halt` is the default