Raspberry hangs, how to understand what's wrong?

Question

Raspberry Pi

Good afternoon, there is Raspberry, a program written by me in Python, a small server on flask.
Sometimes once every 1 day/week it is not at all clear why the Raspberry freezes hard, only a power reset helps.
Symptoms when it freezes:
1. The green and red LEDs are on. During normal operation, the green LED blinks infrequently.
2. Can't connect to my server
3. Can't connect via ssh. It's like the server is offline.
3. Lan flashes - there seems to be a connection.
There is no way to connect the screen to hdmi. Therefore, it is not clear to see whether the raspberry is actually hung or not.
What to watch? Where to dig?

Answer 1

View logs.
If there is nothing in the logs, then iron is the fastest.
First, check if your Raspberry chips are overheating - if they have sufficient cooling.
Try to eliminate overheating by hanging radiators.

Answer 2

My Raspi freezes when it runs out of RAM and linux tries to use the swap file. Perhaps you also have some kind of memory problem, some kind of structure is very swollen in size. In C++, memory leaks are even easier to get

Answer 3

There was the same problem.
Connected from a USB computer - hangs.
Plugged into a socket for a smartphone - it works like a clock
Apparently there was not enough voltage)