Yes, you are right. It was a stack size problem, I actually independently found it out yesterday.
I was forgetting how the stacks in C actually works with function calls.

Anyway, thanks.

I can do better, I can show you the code

https://pastebin.com/ZD6pwKJU

I will try to build a minimal working example later

I'm trying to drive leds with Fastled by sending the data via UDP packets via wifi. The size of the UDP packet is 1024B, that's the biggest that should confortably pass trough all the common routers. So I need 4 packets to get 1024 RGB leds (plus some headers) I want to move the part that receives t...