i have MATEK f405 WING running ArduCopter 3.6.4 with pretty much default setup (minor irrelevant customizations).
I connected Raspberry Pi to the FCs UART1 (Telem1 running mavlink 1 proto). Raspi attempts to establish mavproxy connection with the FC (vi /dev/serial0) but no luck - link down.
The same setup works very well with Pixhawk 2.1 Cube - Raspi connected to Telem2 (via mavproxy).
Not sure if this is a firmware or hardware problem. Tried also uart2 - no luck.
MATEK claims on their website that Telem 1 should be active on UART1