Bob,
My system is debian with internet access. I run the docker version of MC by shiomax, but I am not sure if docker is to blame as a friend of mine who runs a non-docker version has experienced similar problem... My server does not have an audio output as it only serves the music files to other MC clients, by the way.
I deleted the plugins and ran the MC, and the plugins were downloaded but it failed to convert the wma files to mp3.
I tried connecting my iphone to a raspberry pi 4 client. It converted wma files ok, but then it failed to convert many flac files, notably hi-resolution files (96kHz/24bit)... Disabling the transcoding, the iphone can play flac and m4a files ok but no wma files. It seems that the only way for me to play everything on iphone is to use MC26.
Could you check if the conversion works fine on MC27? I set jremote to transcode everything to High (320kbps) quality mp3.