STM32 Code works properly only if 1uF cap is connected between NRST and GND

[LLOLO.1]

Hi, I have encountered strange problem where my code does not work properly on STM32F405RG when there is recommended 100nF cap between NRST and GND pins.

By "working correctly" I mean receiving correct message from USART. I am sending 0xAA and getting 0x44.

When there is 1uF cap instead 100nF the code works fine. What is the problem?

[TDK]

A cap is going to slightly increase the time it takes for the mcu to boot. But 0xAA and 0x44 don't really match up at all. Have to believe the problem is elsewhere.