Do they not work at all or do they simply brake poorly?
Start a plane, get a outside POV, engage reverse... do the engines open up to deploy reverse thrust?
If yes, then you have a problem of weak reverse you can correct editing the .AIR file.
If not and you're sure the assignments were done well, you sure the keys of your keyboard work correctly? I had to trash a lot of keyboards (
current included ASAP) because some keys just randomly got in their... whatever passes for mind to go on momentary strike.
Note:
specifics on .AIR file editing to strengthen reverse thrust will be given on demand. You need it, I tell you. Not much point giving you a something you don't need

There is no such a thing as overkill. Only unworthy targets.