Running JACK 2 with FFADO, the hardware input/output ports are named like system:AP0_dev0_Unknown etc., instead of the usual system:playback_1 etc. as with JACK 1 (or JACK 2 with the ALSA backend).
Apparently the standard port names don't exist even as aliases, so this breaks anything that expects these port names to be present (e.g. Ardour sessions created with JACK 1).
Apart from that, the port numbering is highly inconsistent and confusing:
system:AP0_dev0_Unknown
system:AP1_dev0_Unknown0
system:AP2_dev0_Unknown1
system:AP3_dev0_Unknown2
etc.