Why are rewards changing in value?

The token reward earned from the Miner app always shows a fixed value. However, the indicated USD value on the Miner App may change because it is applying a conversion rate of rewards as US$ equivalent in real-time.

Even rewards in USD stable coins (e.g., USDT) may have values that fluctuate over time vs. US$. You may also use CoinGecko as a reference to the price chart for rewards given by specific campaigns.