Check out "NextRadio - Free FM Radio"
https://play.google.com/store/apps/details?id=com.nextradioapp.nextradio
KitKat and Lollipop compatible and claimed to work on all carriers for the M8.
Go to settings, interface to change to basic radio or else you'll get Internet radio.
If it works, try enhanced mode, you'll get a nice set of tiles for all of your local stations.
Unlike the HTC radio, it won't display RDS data.
It does receive it and will use it to give you an ad to buy the song off of the Internet somewhere. I've never tried it.
If you put it back into basic tuner mode after getting the enhanced list from the Internet, it'll work without touching your network data again and the ads go away.
I've confirmed this by gating it in stages through my root firewall.
I find the M8 radio sensitivity is lower than my previous LTEvo.
If NextRadio works for you but you get reception problems, it's not the app.
It seems to perform just the same as the stock HTC radio.