My non-expert thought is that a 5 day taper for pneumonitis is brief, but obviously I don't know your situation so take this comment for what it is. I developed pneumonitis 30+ days after receiving 54GY of SBRT. For me, pneumonitis caused significant breathing issues and fatigue but I don't recall losing my sense of taste and smell.

I suggest you contact your radiologist about the pneumonitis and prednisone treatment. Don't know how severe your pneumonitis is but I know it needs to be treated for you to recover.