Slide Remote Not Working in RF Mode

I have several Tivos and have Slide Pro remotes to go with them. Lately, they all seem to have reverted from RF mode to infrared, so they won't work when a cabinet door covering the Tivo is closed (as they used to) and they now barely work when pointed right at an unobstructed Tivo.

Does anyone know a fix for this? I've tried to re-pair the remote with the Tivo but that doesn't improve the performance.