PID autotune gives connection error (no replies)

See the below output after doing an M303:

>>> M303 C5 D S205
SENDING:M303 C5 D S205
PID Autotune start
[ERROR] Can't read from printer (disconnected?) (OS Error 6): Device not configured
[ERROR] Can't write to printer (disconnected?) (SerialException): write failed: [Errno 6] Device not configured

The machine has no issues with connectivity, this only happens when doing an M303 PDI autotune. This didn't happen on Marlin 2.0.5.3
Anyone?

It's an SKR 1.3 using baudrate 115200
Serial ports correctly configured