My RFXcom has been working well with HA for many years now.
However suddenly after a Linux kernal update it has stopped working. I believe the /dev/serial/by-id/ is removed for some reason.
Same happened with my Z-Wave dongle but I just had to update the port for it and it started working immediately.
I want to do that with my RFXcom also, but can for the life of me not find where it is configured in HA? Not in the device as was the case with the Z-Wave dongle.
Actually I found a way to change the port via grepping the whole directory: /usr/share/hassio/homeassistant/.storage/core.config_entries
contains the line "device": "/dev/serial/by-id/usb-RFXCOM_RFXtrx433_A1XR21R5-if00-port0"
I changed it to /dev/ttyUSB0, restarted HA and it just works.
I am still baffled why I can not find another (better) place to change it, but I guess this can still help somebody.