I could use some help here;
We have an STM32L475, using blocking UART implementations from Embassy HAL with RTS & CTS.
Rarely we see that flush will NEVER return? That is, the `SR::tc` bit will never go high. 
What can cause this behaviour apart from CTS never going high?

By now we are kinda desperate, as it is hitting production units in the wild, and the result is a complete block of all code :/