Hi,
I’m looking at variant.cpp for SAMD21 Dev board package 1.6.19.
The Pin Description for g_APinDescription[25] is entered as PortA 31 which is SWDIO, but the comments say it should be RX_LED PB03. This must be a mistake. As such the macro PIN_LED_RXL will actually be addressing the SWDIO pin.
Cheers