@User @User I just realised I had a clock constraint on the UART RX line. That, together with a high clock tree delay results in loads of delay buffers on the UART RX input, which seems silly. Is it ok to leave the pin unconstrained? It is after all asynchronous, so we shouldn't care about the signal lining up with the clock. Can I leave the TX line unconstrained too?

Sorry, this question is beyond my expertise.

@User mine too! 🙂