Thanks a lot for the detailed feedback!
It looks like we were not only missing the kernel driver but also the brcmfmac43455-sdio.bin file - we'll include that in the next release.
You'll still have to take care about the brcmfmac43455-sdio.txt file yourself, but adding just that single file to the my-firmware directory and sticking to the kernel overlay mechanism should be fine I guess (this file is not only missing in Linux mint but also in the linux kernel firmware repository so there's not much we can do about it for now).
As for the kodi crash: If it wasn't a one-off glitch and you are able to reproduce that please open a ticket with some more information here: Ticket System - LibreELEC Forum with a link to your log. Best use the logfile upload function in LibreELEC settings, that will upload all relevant logs including the kodi_crash.log file with hopefully some useful information.
so long,
Hias